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Objective: Reno-renal reflexes are disturbed in cardiovascular and hypertensive conditions when elevated levels of pro-inflammatory mediators/cytokines are present within the kidney. We hypothesised that exogenously administered inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interleukin (IL)-1β modulate the renal sympatho-excitatory response to chemical stimulation of renal pelvic sensory nerves., Methods: In anaesthetised rats, intrarenal pelvic infusions of vehicle [0.9% sodium chloride (NaCl)], TNF-α (500 and 1000 ng/kg) and IL-1β (1000 ng/kg) were maintained for 30 min before chemical activation of renal pelvic sensory receptors was performed using randomized intrarenal pelvic infusions of hypertonic NaCl, potassium chloride (KCl), bradykinin, adenosine and capsaicin., Results: The increase in renal sympathetic nerve activity (RSNA) in response to intrarenal pelvic hypertonic NaCl was enhanced during intrapelvic TNF-α (1000 ng/kg) and IL-1β infusions by almost 800% above vehicle with minimal changes in mean arterial pressure (MAP) and heart rate (HR). Similarly, the RSNA response to intrarenal pelvic adenosine in the presence of TNF-α (500 ng/kg), but not IL-1β, was almost 200% above vehicle but neither MAP nor HR were changed. There was a blunted sympatho-excitatory response to intrapelvic bradykinin in the presence of TNF-α (1000 ng/kg), but not IL-1β, by almost 80% below vehicle, again without effect on either MAP or HR., Conclusion: The renal sympatho-excitatory response to renal pelvic chemoreceptor stimulation is modulated by exogenous TNF-α and IL-1β. This suggests that inflammatory mediators within the kidney can play a significant role in modulating the renal afferent nerve-mediated sympatho-excitatory response., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Proper fluid resuscitation can relieve visceral damage and improve survival in severely burned patients. This study compared the effectiveness of resuscitation with 400mEq/L hypertonic saline (HS) and sodium lactate Ringer's solution (LR) in rats with kidney injury caused by burn trauma., Methods: Rats (Sprague-Dawley) underwent burn injury and were randomized into sham, LR, and HS groups. Samples from the kidney were assayed for water content ratio, histopathology, and oxidative stress (superoxide dismutase (SOD) and malondialdehyde (MDA)). Serum sodium, renal function (creatinine and cystatin (Cys)-C), and inflammatory response (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and high mobility group protein box (HMGB)-1) were also examined as serum markers., Results: Hypertonic saline resuscitation reduced the renal water content ratio and improved renal histopathology caused by severe burns. This effect was accompanied by reductions in serum creatinine and Cys-C as well as TNF-α, IL-1β, and HMGB1. Serum sodium concentration and SOD activity were increased, whereas MDA content was decreased in the kidney tissue of the HS group., Conclusions: The data indicate that 400mEq/L HS solution reduces hyponatremia and renal edema, inhibits the release of inflammatory mediators, and alleviates oxidative stress injury, thus protecting against kidney injury induced by severe burns., (Copyright © 2018 Elsevier Ltd and ISBI. All rights reserved.)

Purpose:: To evaluate the effects of hypertonic saline solution associated to remote ischemic perconditioning in renal ischemia/reperfusion injury in rats., Methods:: Twenty five male rats (Wistar) underwent right nephrectomy and were distributed into five groups: Sham group (S); Ischemia/Reperfusion group (I/R) with 30 minutes of renal ischemia; Remote ischemic perconditioning group (Per) with three cycles of 10 minutes of I/R performed during kidney ischemia; Hypertonic saline solution group (HSS) treated with hypertonic saline solution (4ml/kg); remote ischemic perconditioning + Hypertonic saline solution group (Per+HSS) with both treatments. After reperfusion, blood samples were collected for BUN and creatinine serum levels analyzes. TBARS were evaluated in plasma and renal tissue to assess oxidative stress. Kidney histopathological examination were performed., Results:: Per+HSS group showed a lower degree of renal dysfunction in relation to I/R group, whereas the technique of remote ischemic perconditioning isolated or associated with saline solution significantly reduced oxidative stress and histological damage., Conclusion:: Remote ischemic perconditioning associated or not to saline solution promoted reduction of acute renal injury induced by ischemia/reperfusion.

The present study aimed to investigate the potential physiological role of vasopressin and the incretin hormone of the gastrointestinal tract (glucagon-like peptide-1; GLP-1) in the regulation of the water-salt balance in a hyperosmolar state as a result of sodium loadings. In rats, the administration of hypertonic NaCl solution resulted in a significant increase in natriuresis, which correlated with the vasopressin excretion rate. Natriuresis following an i.p. NaCl load (23.2 ± 1.4 μmol/min/kg) was enhanced by inhibition of V2 receptors (51.6 ± 3.7 μmol/min/kg, P < 0.05) and was reduced by a V1a antagonist injection (6.3 ± 1.1 μmol/min/kg, P < 0.05). Compared to i.p. salt administration, oral NaCl loading induced a significant increase in the plasma GLP-1 level within 5 min and resulted in more prominent natriuresis and a smaller increase in blood sodium concentration. It was hypothesised that the basis for the fast elimination of excess sodium following an oral NaCl load could be the involvement of GLP-1 in osmoregulation combined with vasopressin. It was demonstrated that GLP-1 mimetic exenatide (1.5 nmol/kg) produced a significant decrease in proximal reabsorption and an increase in fractional sodium excretion (from 0.15 ± 0.04% to 9 ± 1%). It was also shown that vasopressin at doses of 1-10 μg/kg and the selective V1a agonist (1 μg/kg) induced an increase in sodium fractional excretion to 10 ± 2% and 8 ± 2%, respectively. Combined administration of exenatide and V1a agonist revealed their cumulative natriuretic effect, and sodium fractional excretion increased by up to 18 ± 2%. These data suggest that GLP-1 combined with vasopressin could be involved in the regulation of sodium balance in the hyperosmolar state as a result of NaCl loading. Vasopressin regulates the reabsorption of a significant portion of filtered sodium in the distal segment of the nephron and modulates the natriuretic effect of GLP-1., (© 2016 British Society for Neuroendocrinology.)

Hypertonic NaCl infused into the carotid arteries increases mean arterial pressure (MAP) and changes sympathetic nerve activity (SNA) via cerebral mechanisms. We hypothesized that elevated sodium levels in the blood supply to the brain would induce differential responses in renal and cardiac SNA via sensors located outside the blood-brain barrier. To investigate this hypothesis, we measured renal and cardiac SNA simultaneously in conscious sheep during intracarotid infusions of NaCl (1.2 M), sorbitol (2.4 M), or urea (2.4 M) at 1 ml/min for 4 min into each carotid. Intracarotid NaCl significantly increased MAP (91 ± 2 to 97 ± 3 mmHg, P < 0.05) without changing heart rate (HR). Intracarotid NaCl was associated with no change in cardiac SNA (11 ± 5.0%), but a significant inhibition of renal SNA (-32.5 ± 6.4%, P < 0.05). Neither intracarotid sorbitol nor urea changed MAP, HR, central venous pressure, cardiac SNA, and renal SNA. The changes in MAP and renal SNA were completely abolished by microinjection of the GABA agonist muscimol (5 mM, 500 nl each side) into the paraventricular nucleus of the hypothalamus (PVN). Infusion of intracarotid NaCl for 20 min stimulated a larger increase in water intake (1,100 ± 75 ml) than intracarotid sorbitol (683 ± 125 ml) or intracarotid urea (0 ml). These results demonstrate that acute increases in blood sodium levels cause a decrease in renal SNA, but no change in cardiac SNA in conscious sheep. These effects are mediated by cerebral sensors located outside the blood-brain barrier that are more responsive to changes in sodium concentration than osmolality. The renal sympathoinhibitory effects of sodium are mediated via a pathway that synapses in the PVN.

Introduction: The recent success of renal denervation in lowering blood pressure in drug-resistant hypertensive patients has stimulated interest in developing novel approaches to renal denervation including local drug/chemical delivery. The purpose of this study was to develop a rat model in which depletion of renal norepinephrine (NE) could be used to determine the efficacy of renal denervation after the delivery of a chemical to the periadventitial space of the renal artery., Methods: Renal denervation was performed on a single renal artery of 90 rats (n = 6 rats/group). The first study determined the time course of renal denervation after surgical stripping of a renal artery plus the topical application of phenol in alcohol. The second study determined the efficacy of periadventitial delivery of hypertonic saline, guanethidine, and salicylic acid. The final study determined the dose-response relationship for paclitaxel. In all studies, renal NE content was determined by liquid chromatography-mass spectrometry., Results: Renal NE was depleted 3 and 7 days after surgical denervation. Renal NE was also depleted by periadventitial delivery of all agents tested (hypertonic saline, salicylic acid, guanethidine, and paclitaxel). A dose response was observed after the application of 150 μL of 10(-5) M through 10(-2) M paclitaxel., Conclusion: We developed a rat model in which depletion of renal NE was used to determine the efficacy of renal denervation after perivascular renal artery drug/chemical delivery. We validated this model by demonstrating the efficacy of the neurotoxic agents hypertonic saline, salicylic acid, and guanethidine and increasing doses of paclitaxel.

Objective: Analysis of renal excretory system integrity and efficacy of radiofrequency ablation with and without irrigation with saline at 2°C (SF2)., Materials and Methods: The median third of sixteen kidneys were submitted to radiofrequency (exposition of 1 cm) controlled by intra-surgical ultrasound, with eight minutes cycles and median temperature of 90°C in eight female pigs. One excretory renal system was cooled with SF2, at a 30mL/min rate, and the other kidney was not. After 14 days of post-operatory, the biggest diameters of the lesions and the radiological aspects of the excretory system were compared by bilateral ascending pyelogram and the animals were sacrificed in order to perform histological analysis., Results: There were no significant differences between the diameters of the kidney lesions whether or not exposed to cooling of the excretory system. Median diameter of the cooled kidneys and not cooled kidneys were respectively (in mm): anteroposterior: 11.46 vs. 12.5 (p = 0.23); longitudinal: 17.94 vs. 18.84 (p = 0.62); depth: 11.38 vs. 12.25 (p = 0.47). There was no lesion of the excretory system or signs of leakage of contrast media or hydronephrosis at ascending pyelogram., Conclusion: Cooling of excretory system during radiofrequency ablation does not sig¬nificantly alter generated coagulation necrosis or affect the integrity of the excretory system in the studied model.

Background: The renal distal nephron plays an important role in the maintenance of sodium balance, extra cellular volume and blood pressure. The degree of water transport, via aquaporin2 water channels (AQP2), and sodium transport, via epithelial sodium channels (ENaC) in renal collecting duct principal cells are reflected by the level of urinary excretion of AQP2 (u-AQP2) and the γ-fraction of ENaC (u-ENaCγ). The effects of an acute intravenous volume load with isotonic saline, hypertonic saline and glucose on u-AQP2, u-ENaCγ and underlying mechanisms have never been studied in a randomized, placebo-controlled trial in healthy humans., Methods: We studied the effects of 0.9% saline (23 ml/kg), 3% saline (7 ml/kg) and 5% glucose (23 ml/kg) on u-AQP2 and u-ENaCγ, fractional sodium excretion (FENa), free water clearance (CH2O), and plasma concentrations of vasopressin (AVP), renin (PRC), angiotensin II (ANG II) and aldosterone (Aldo) in a randomized, crossover study of 23 healthy subjects, who consumed a standardized diet, regarding calories, sodium and fluid for 4 days before each examination day., Results: After isotonic saline infusion, u-AQP2 increased (27%). CH2O and u-ENaCγ were unchanged, whereas FENa increased (123%). After hypertonic saline infusion, there was an increase in u-AQP2 (25%), u-ENaCγ (19%) and FENa (96%), whereas CH2O decreased (-153%). After isotonic glucose infusion, there was a decrease in u-AQP2 (-16%), ENaCγ (-10%) and FENa (-44%) whereas CH2O increased (164%). AVP remained unchanged after isotonic saline and glucose, but increased after hypertonic saline (139%). PRC, AngII and p-Aldo decreased after isotonic and hypertonic saline infusion, but not after glucose infusion., Conclusions: Volume expansion with 3% and 0.9% saline increased u-AQP2, while isotonic glucose decreased u-AQP2. Infusion of hypertonic saline increased u-ENaCγ, whereas u-ENaCγ was not significantly changed after isotonic saline and tended to decrease after glucose. Thus, the transport of water and sodium is changed both via the aquaporin 2 water channels and the epithelial sodium channels during all three types of volume expansion to regulate and maintain water- and sodium homeostasis in the body., Trial Registration: Clinical Trial no: NCT01414088.

Renal vasodilation and sympathoinhibition are recognized responses induced by hypernatremia, but the central neural pathways underlying such responses are not yet entirely understood. Several findings suggest that A2 noradrenergic neurons, which are found in the nucleus of the solitary tract (NTS), play a role in the pathways that contribute to body fluid homeostasis and cardiovascular regulation. The purpose of this study was to determine the effects of selective lesions of A2 neurons on the renal vasodilation and sympathoinhibition induced by hypertonic saline (HS) infusion. Male Wistar rats (280-350 g) received an injection into the NTS of anti-dopamine-beta-hydroxylase-saporin (A2 lesion; 6.3 ng in 60 nl; n = 6) or free saporin (sham; 1.3 ng in 60 nl; n = 7). Two weeks later, the rats were anesthetized (urethane 1.2 g⋅kg(-1) b.wt., i.v.) and the blood pressure, renal blood flow (RBF), renal vascular conductance (RVC) and renal sympathetic nerve activity (RSNA) were recorded. In sham rats, the HS infusion (3 M NaCl, 1.8 ml⋅kg(-1) b.wt., i.v.) induced transient hypertension (peak at 10 min after HS; 9±2.7 mmHg) and increases in the RBF and RVC (141±7.9% and 140±7.9% of baseline at 60 min after HS, respectively). HS infusion also decreased the RSNA (-45±5.0% at 10 min after HS) throughout the experimental period. In the A2-lesioned rats, the HS infusion induced transient hypertension (6±1.4 mmHg at 10 min after HS), as well as increased RBF and RVC (133±5.2% and 134±6.9% of baseline at 60 min after HS, respectively). However, in these rats, the HS failed to reduce the RSNA (115±3.1% at 10 min after HS). The extent of the catecholaminergic lesions was confirmed by immunocytochemistry. These results suggest that A2 noradrenergic neurons are components of the neural pathways regulating the composition of the extracellular fluid compartment and are selectively involved in hypernatremia-induced sympathoinhibition.

TonEBP/NFAT5 transcription factor is a master regulator of genes involved in osmoprotection. Cyclooxygenase 2 (COX2) has been reported to be a cytoprotective molecule in the inner renal medulla, where cells are physiologically exposed to the highest osmolality of the body. Our aim was to study whether COX2 expression requires TonEBP/NFAT5. Incubation of MDCK cells in hypertonic NaCl medium (500 mOsm/kg H2O) caused fully translocation of TonEBP/NFAT5 from cytoplasm to nucleoplasm and significantly increased COX2 mRNA, protein and activity levels. TonEBP/NFAT5-siRNA prevented hypertonic induction of COX2 mRNA and protein, leading to a depressed-prostaglandin synthesis and to a decreased cell survival. By using COX2-siRNA and COX2 specific inhibitor NS398, we found that cell survival does not depend on endogenous COX2-induced prostaglandin synthesis, but that cytoprotection strongly correlates with COX2 protein levels. These results demonstrate a new function for TonEBP/NFAT5, i.e., to mediate hypertonic-induced COX2 expression, and suggest that osmoprotection strongly depends on COX2 protein levels.

Background and Purpose: To evaluate the possibility of shrinking the kidney by perfusion with hypertonic solution to facilitate organ removal in laparoscopic surgery., Materials and Methods: After 18 open nephrectomies (ONs) in 9 pigs, one of four saline solutions (5%, 7.5%, 10%, and 15%) was infused through a catheter into the renal artery for 5 minutes in four kidneys each. The volumes and weights of the kidneys were measured before and after renal perfusion; the kidneys were then sent for histologic evaluation. Eight ONs were performed, and the kidneys were removed from the abdominal cavity in a plastic bag in order to mimic organ entrapment during laparoscopy. The kidneys were perfused with hypertonic solution and were again put in a plastic bag and removed from the same animal's abdomen through another incision. The incisions were measured with calipers before and after extraction of the unperfused and perfused organs., Results: The kidneys that underwent perfusion with 5% saline had the greatest decrease in both weight and volume, an average of 16% and 17.8%, respectively. The average incision needed for extraction of unperfused kidneys was 44.9 mm (range 40-58 mm), whereas the mean size of the incision needed to remove perfused kidneys was 26.6 mm (range 20-30 mm) (P < 0.001). The relative reduction in the necessary incision size therefore was 44.3% (range 33.3%-55%)., Conclusion: Perfusion with 5% saline is able to shrink the kidney volume slightly with mild histologic changes. In the pig, it is possible to decrease the renal incision necessary for kidney removal by 44% using this method.

Experiments conducted in vitro suggest that high osmolality stimulates endothelin production and release by renal tubular epithelial cells. Whether hyperosmotic solutions exert similar effects in vivo is unknown. Therefore, we tested the hypothesis that increasing renal medullary osmolality enhances urinary excretion of endothelin in anesthetized rats. Isosmotic NaCl (284 mosmol/kgH(2)O) was infused either intravenously (1.5 ml/h) or into the renal medullary interstitium (0.5 ml/h) during a 1-h equilibration period and 30-min baseline urine collection period, followed by either isosmotic or hyperosmotic NaCl (921 or 1,664 mosmol/kgH(2)O iv; 1,714 mosmol/kgH(2)O into renal medulla) for two further 30-min periods. Compared with isosmotic NaCl, infusion of hyperosmotic NaCl into the renal medulla significantly increased the endothelin excretion rate (P < 0.05; from 0.30 +/- 0.02 to 0.49 +/- 0.03 fmol/min). Intravenous infusion of hyperosmotic NaCl also significantly increased endothelin excretion rate in a concentration-dependent manner (from 0.79 +/- 0.07 to 1.77 +/- 0.16 fmol/min and 0.59 +/- 0.04 to 1.11 +/- 0.08 fmol/min for 1,664 and 921 mosmol/kgH(2)O, respectively). To differentiate between effects of osmolality and NaCl, similar experiments were performed using mannitol solutions. Compared with isosmotic mannitol, medullary interstitial infusion of hyperosmotic mannitol (1,820 mosmol/kgH(2)O) significantly increased endothelin excretion rate (P < 0.05; from 0.54 +/- 0.03 to 0.94 +/- 0.12 fmol/min). Thus exposing the renal medulla to hyperosmotic concentrations of either NaCl or mannitol stimulates endothelin release in vivo, consistent with medullary osmolality being an important regulator of renal endothelin synthesis.

The mechanism by which blood pressure rises in the SHR strain remains to be elucidated. Also, there is a surprising lack of experimental data on the natriuretic mechanisms induced by intracerebroventricular (ICV) injection of hyperosmotic saline (HoS) in SHR. In normotensive animals ICV injection of HoS causes coordinated responses including natriuresis and inhibition of renal sympathetic nerve activity. In the present study, we hypothesized that presumable blunting of the sympathoinhibitory response to centrally injected HoS may contribute to a lack of suppression of efferent renal nerve outflow in SHR. To test this hypothesis, the present study evaluates the influence of renal denervation after central HoS injection at increasing concentration on urinary sodium handling in SHR compared with age-matched normotensive WKy rats. The study confirmed previous data showing pronounced natriuretic response to centrally HoS stimuli but also demonstrated that the creatinine clearance (C(Cr)) and fractional sodium excretion responses diminished as graded NaCl concentrations were increased in WKy rats but not in SHR. In SHR, increased FE(Na) obtained by central administration of 0.90 M NaCl was produced by increases in proximal (FEP(Na)) and post-proximal fractional urinary sodium rejection without changes in C(Cr), indicating a direct tubular effect. Renal denervation caused significant antinatriuresis by decreased C(Cr) and increased FEP(Na) reabsorption in WKy but not in SHR. This study suggests that natriuresis observed only after higher centrally HoS stimuli with a rightward shift of dose-response curve provides evidence of a down-regulation of target organ responsiveness of periventricular areas of genetic hypertensive rats.

Aim: This study focused on static and dynamic changes in total renal blood flow (RBF) during volume expansion and tested whether a change in RBF characteristics is a necessary effector mechanism in saline-induced natriuresis., Methods: The aortic flow subtraction technique was used to measure RBF continuously. Identical amounts of NaCl (2.4 mmol kg(-1)) were given as slow isotonic (Iso, 120 min), slow hypertonic (Hyper, 120 min), and rapid isotonic loads (IsoRapid, 30 min)., Results: During Iso and IsoRapid, arterial blood pressure increased slightly (6-7 mmHg), and during Hyper it remained unchanged. Iso and Hyper increased sodium excretion (4 +/- 1 to 57 +/- 27 and 10 +/- 4 to 79 +/- 28 micromol min(-1), respectively) and decreased plasma renin activity (by 38% and 29%), angiotensin II (by 56% and 58%) and aldosterone (by 47% and 65%), while RBF remained unchanged. IsoRapid caused a similar increase in sodium excretion (to 72 +/- 19 micromol min(-1)), a similar decrease in renin system activity, but a 15% elevation of RBF (282 +/- 22 to 324 +/- 35 mL min(-1)). Selected frequency domain parameters of RBF autoregulation did not change in response to any load., Conclusions: In response to slow saline loading simulating daily sodium intake, the rate of sodium excretion may increase 10-20-fold without any change in mean arterial blood pressure or in RBF. Regulatory responses to changes in total body NaCl levels appears, therefore, to be mediated primarily by neurohumoral mechanisms and may occur independent of changes in arterial pressure or RBF.

Background: Decompensated hemorrhagic shock is often refractory to resuscitation, and we show here that it is associated with loss of vascular tone in skeletal muscle precapillary arterioles. We tested the hypothesis that microvascular derangements in the skeletal muscle, intestinal, and renal microcirculation systems would be reversed by initial hypertonic saline-dextran infusion., Methods: Male Sprague-Dawley rats underwent precollicular brain stem transection without anesthesia for study. Parameters measured by in vivo videomicroscopy included cardiac output, mean arterial pressure, and microvascular responses in the skeletal muscle, ileum, and renal (i.e., the hydronephrotic kidney) microcirculation systems. Hemorrhaged was induced to a mean arterial pressure of 50 mmHg until decompensation occurred. The rats were then initially resuscitated with (1) 4 mL/kg 7.5% NaCl in 6% dextran 70, (2) 33 mL/kg .9% NaCl in 6% dextran 70, or (3) 33 mL/kg .9% NaCl. Twenty minutes later they received shed blood plus 33 mL/kg .9% NaCl to maintain mean arterial pressure at baseline levels., Results: Decompensated hemorrhagic shock decreased cardiac output to between 24% and 35% of baseline values and profoundly decreased microvascular blood flow to between 10% and 19% of baseline. At the completion of resuscitation cardiac output increased to greater than baseline in all groups. Microvascular blood flow increased toward baseline transiently but then progressively deteriorated to between 36% and 69% of baseline in the 3 tissues. There was no significant difference between the three resuscitative fluids., Conclusions: Despite return of cardiac output to greater than baseline levels, muscle, intestinal, and renal microvascular blood flows remained significantly depressed. Hypertonic saline and/or dextran did not improve these deficits.

Background: Aquaporin-2 (AQP-2) is an arginine vasopressin (AVP)-regulated water channel in kidney collecting duct cells. The present study was undertaken to determine whether a change in tonicity could directly regulate the AQP-2 gene in an in vitro experiment., Methods: Various fragments of the 5'-flanking region of the murine AQP-2 gene up to -9.5 kb were cloned into a luciferase (Luc) reporter plasmid, and they were transiently transfected into Madin-Darby canine kidney cells., Results: Hypertonicity significantly increased the Luc activity of the constructs containing >6.1 kb of the 5'-flanking region of the AQP-2 gene (-6.1AQP2). However, promoter regions <4.3 kb in length containing the tonicity-responsive enhancer (TonE) at bp -570 to -560 were not stimulated by hypertonicity. The TonE-deleted construct which contains -9.5 to -1.1 kb of the 5' side of the AQP-2 gene, 8.4AQP2, was also stimulated by hypertonicity. Mitogen-activated protein (MAP) kinase inhibitors SB203580 and U0126 did not affect the Luc activity of -6.1AQP2 induced by hypertonicity. In addition, the vector expressing dominant-negative TonE-binding protein (TonEBP) did not affect the hypertonicity-induced Luc activity of -6.1AQP2. The Luc activity of -6.1AQP2 was stimulated by the overexpression of TonEBP. Hypertonicity further increased the Luc activity of -6.1AQP2 under the overexpression of TonEBP., Conclusion: These findings indicate that hypertonicity regulates AQP-2 promoter activity via an AVP-independent mechanism, and that the tonicity-responsive element resides between the -6.1 and -4.3 kb 5'-flanking region of the AQP-2 gene, in which the structure and mechanism of response to hypertonicity could be distinct from those of TonE.

Purpose: To evaluate histological changes in normal renal tissue induced by the injection of a hypertonic liquid., Materials and Methods: Transarterial injection was performed in 17 healthy rabbits at various rates of infusion and amounts of isotonic and hypertonic (7%) sodium chloride solutions. In group 1, 10 cc of isotonic sodium chloride solution was injected. In groups 2 and 3, 1-10 cc of hypertonic solution was injected at rates of 1.0 cc/sec and 0.05 cc/sec, respectively. After 20 minutes of hemostasis, renal weight measurements and histological examinations were performed. In three rabbits that received 10 cc of 7% sodium chloride, lung samples were also obtained, and histological changes were reviewed., Results: There was no tissue injury in group 1, and in groups 2 and 3 the histological changes for infusions of 4-10 cc were greater than those of 1-3 cc. There was no vascular endothelial cell damage in any case. None of the histological changes were dose dependent, and the lungs showed no clear histological alterations., Conclusion: Higher doses of a hypertonic sodium chloride solution cause irreversible histological changes in the rabbit kidney.

In response to ambient hypertonicity, TonEBP (tonicity-responsive enhancer binding protein) stimulates certain genes including those encoding cytokines, transporters for organic solutes, and a molecular chaperone. TonEBP is regulated in a bidirectional manner, upregulated by an increase in ambient tonicity while downregulated by a decrease. To investigate the role of intracellular ionic strength in the activity of TonEBP, we subjected Madin-Darby canine kidney cells to a variety of conditions. Electron microprobe analysis was performed to measure intracellular electrolytes. Under conditions in which changes in cell volume were similar, TonEBP activity correlated with the intracellular ionic strength regardless of the external tonicity. On the other hand, inhibition of the Na+/K+-ATPase and high external K+ concentration led to a decreased activity of TonEBP despite a marked increase in the intracellular ionic strength. Because isotonic swelling is known to occur under these conditions, these data suggest that dilution of the cytoplasmic constituents inhibits the activity of TonEBP. We conclude that intracellular ionic strength and water content are major factors that determine the activity of TonEBP.

Objective: To examine, in young pigs, changes in baseline pelvic pressure and diuresis in the contralateral kidney during conditions of increasing pelvic pressure and perfusion with isotonic saline in the ipsilateral renal pelvis; the role of a reno-renal nervous mechanism was examined by denervating the kidneys, and the effect of bladder filling on these variables assessed., Materials and Methods: Female pigs (37-40 kg) were assessed under general anaesthesia. Transparenchymally, one 6 F and two 6 F catheters were introduced into the right and left renal pelvis, respectively. Through a bladder incision an 8 F catheter was introduced 10 cm into the right ureter to collect urine and the orifice closed around the catheter. For bladder drainage and to measure bladder pressure a 10 F catheter was placed in the bladder and both the 8 F and 10 F catheters lead out through the urethra. In group A, five animals served as controls, with group B comprising eight with intact nerves and group C eight with denervated kidneys. In group B and C the left renal pelvis was perfused with isotonic saline at 2, 4, 6, 8, 10, 12 and 16 mL/min while the bilateral pelvic pressure and right renal diuresis were recorded; the bladder was kept empty and 0.5 h later the left pelvis was perfused with 10 mL/min while the bladder catheter was closed. Perfusion continued until micturition occurred. The bilateral pelvic pressure, bladder pressure and right renal diuresis were recorded. In group C the kidneys were surgically denervated, dividing all adhesions and all connective tissue around the pelvis and the vascular pedicle. The renal artery was freed to the aortic level., Results: During the pressure-perfusion study the mean (sd) right pelvic pressure was 7.4 (0.2) mmHg in group B and 8.6 (0.2) mmHg in group C. The diuresis from the right kidney in both groups was similar and the same as that in group A. The perfusion rate and pressure on the left side had no influence on pelvic pressure and diuresis on the right side. During perfusion with a full bladder the right pelvic pressure was 8.6 mmHg in group B and 9.5 mmHg in group C. Diuresis in group B was approximately 0.6 mL/min and a little higher in group C, at approximately 1 mL/min, but identical to that in group A., Conclusion: These results indicate that a reno-renal reflex mechanism has no apparent role in young pigs during pressure-perfusion measurements with an empty or full bladder.

Renal responses were quantified in northern elephant seal (Mirounga angustirostris) pups during their postweaning fast to examine their excretory capabilities. Pups were infused with either isotonic (0.9%; n = 8; Iso) or hypertonic (16.7%; n = 7; Hyper) saline via an indwelling catheter such that each pup received 3 mmol NaCl/kg. Diuresis after the infusions was similar in magnitude between the two treatments. Osmotic clearance increased by 37% in Iso and 252% in Hyper. Free water clearance was reduced 3.4-fold in Hyper but was not significantly altered in Iso. Glomerular filtration rate increased 71% in the 24-h period after Hyper, but no net change occurred during the same time after Iso. Natriuresis increased 3.6-fold in Iso and 5.3-fold in Hyper. Iso decreased plasma arginine vasopressin (AVP) and cortisol acutely, whereas Hyper increased plasma and excreted AVP and cortisol. Iso was accompanied by the retention of water and electrolytes, whereas the Hyper load was excreted within 24 h. Natriuresis is attributed to increased filtration and is independent of an increase in atrial natriuretic peptide and decreases in ANG II and aldosterone. Fasting pups appear to have well-developed kidneys capable of both extreme conservation and excretion of Na(+).

The lamina terminalis is situated in the anterior wall of the third ventricle and plays a major role in fluid and electrolyte homeostasis and cardiovascular regulation. The present study examined whether the effects of intracerebroventricular infusion of hypertonic saline and ANG II on renal sympathetic nerve activity (RSNA) were mediated by the lamina terminalis. In control, conscious sheep (n = 5), intracerebroventricular infusions of 0.6 M NaCl (1 ml/h for 20 min) and ANG II (10 nmol/h for 30 min) increased mean arterial pressure (MAP) by 6 +/- 1 (P < 0.001) and 14 +/- 3 mmHg (P < 0.001) and inhibited RSNA by 80 +/- 6 (P < 0.001) and 89 +/- 7% (P < 0.001), respectively. Both treatments reduced plasma renin concentration (PRC). Intracerebroventricular infusion of artificial cerebrospinal fluid (1 ml/h for 30 min) had no effect. In conscious sheep with lesions of the lamina terminalis (n = 6), all of the responses to intracerebroventricular hypertonic saline and ANG II were abolished. In conclusion, the effects of intracerebroventricular hypertonic saline and ANG II on RSNA, PRC, and MAP depend on the integrity of the lamina terminalis, indicating that this site plays an essential role in coordinating the homeostatic responses to changes in brain Na(+) concentration.

The hypothesis that natriuresis can be induced by stimulation of gastrointestinal osmoreceptors was tested in eight supine subjects on constant sodium intake (150 mmol NaCl/day). A sodium load equivalent to the amount contained in 10% of measured extracellular volume was administered by a nasogastric tube as isotonic or hypertonic saline (850 mM). In additional experiments, salt loading was replaced by oral water loading (3.5% of total body water). Plasma sodium concentration increased after hypertonic saline (+3.1 +/- 0.7 mM), decreased after water loading (-3.8 +/- 0.8 mM), and remained unchanged after isotonic saline. Oncotic pressure decreased by 9.4 +/- 1.2, 3.7 +/- 1.2, and 10.7 +/- 1.3%, respectively. Isotonic saline induced an increase in renal sodium excretion (104 +/- 15 to 406 +/- 39 micromol/min) that was larger than seen with hypertonic saline (85 +/- 15 to 325 +/- 39 micromol/min) and water loading (88 +/- 11 to 304 +/- 28 micromol/min). Plasma ANG II decreased to 22 +/- 6, 35 +/- 6, and 47 +/- 5% of baseline after isotonic saline, hypertonic saline, and water loading, respectively. Plasma atrial natriuretic peptide (ANP) concentrations and urinary excretion rates of endothelin-1 were unchanged. In conclusion, stimulation of osmoreceptors by intragastric infusion of hypertonic saline is not an important natriuretic stimulus in sodium-replete subjects. The natriuresis after intragastric salt loading was independent of ANP but can be explained by inhibition of the renin-angiotensin system.

The hypothesis that renal sodium handling is controlled by changes in plasma sodium concentration was tested in seated volunteers. A standard salt load (3.08 mmol/kg body wt over 120 min) was administered as 0.9% saline (Isot) or as 5% saline (Hypr) after 4 days of constant sodium intake of 75 (LoNa+) or 300 mmol/day (HiNa+). Hypr increased plasma sodium by approximately 4 mmol/l but increased plasma volume and central venous pressure significantly less than Isot irrespective of diet. After LoNa+, Hypr induced a smaller increase in sodium excretion than Isot (48 +/- 8 vs. 110 +/- 17 micromol/min). However, after HiNa+ the corresponding natriureses were identical (135 +/- 33 vs. 139 +/- 39 micromol/min), despite significant difference between the increases in central venous pressure. Decreases in plasma ANG II concentrations of 23-52% were inversely related to sodium excretion. Mean arterial pressure, plasma oxytocin and atrial natriuretic peptide concentrations, and urinary excretion rates of endothelin-1 and urodilatin remained unchanged. The results indicate that an increase in plasma sodium may contribute to the natriuresis of salt loading when salt intake is high, supporting the hypothesis that osmostimulated natriuresis is dependent on sodium balance in normal seated humans.

To determine the overall gain of the hepatorenal reflex, hypertonic NaCl solutions were infused into the portal vein or inferior vena cava of anesthetized dogs at a rate of 0.01 ml/kg/min for 30 min and the urinary Na excretion measured. Infusion of 2.25% NaCl into either the portal vein or inferior vena cava had no effect. Portal infusion of 4.5% or 9% NaCl produced an increase of 36 +/- 16 or 40 +/- 17 microeq/kg/30 min, respectively, while inferior vena caval infusion had no effect. With 13.5% NaCl infusion, a significant increase in the natriuretic response was seen with portal venous infusion, with no significant difference between portal venous and inferior vena caval infusion. Thus, the difference in the natriuretic response between portal venous and inferior vena caval infusion was dependent on the degree of input; when an appropriate input was given, natriuresis was induced only by portal venous infusion, probably mediated by the hepatorenal reflex. The gain of the hepatorenal reflex was calculated from the output divided by the input. When 4.5% or 9% NaCl was infused into the portal vein, the 2-h gain of the hepatorenal reflex was 0.38 +/- 0.15 or 0.34 +/- 0.14, respectively.

In antidiuresis, the cells of the renal medulla are exposed to high extracellular concentrations of NaCl and urea. Since urea equilibrates with the intracellular compartment and is known to perturb intracellular macromolecules, high urea concentrations may well disturb the structure and function of cell proteins. Two types of organic substances are believed to counteract the adverse effects of high intracellular urea concentrations: specific organic osmolytes of the trimethylamine family [betaine and glycerophosphorylcholine (GPC)], which accumulate in renal medullary cells during prolonged periods of antidiuresis and cytoprotective heat shock proteins (HSPs), the tissue content of two of which (HSPs 27 and 72) is much higher in the inner medulla than in the iso-osmotic renal cortex. To evaluate the contribution of trimethylamines and HSPs to cytoprotection in the presence of high urea concentrations, the effect of HSP induction and osmolyte accumulation prior to exposure to high urea concentrations was examined in Madin-Darby canine kidney (MDCK) cells. Accumulation of organic osmolytes and synthesis of HSP27 and HSP72 was initiated by hypertonic stress (increasing the osmolality of the medium from 290 to 600 mosmol/kg H2O by NaCl addition). Control, non-conditioned cells remained in the isotonic medium for the same period. Upon subsequent exposure to an additional 600 mM urea in the medium for 24 h, 90% of the osmotically conditioned cells but only 15% of non-conditioned cells survived. The HSP72 and trimethylamine contents of the NaCl-conditioned MDCK cells, but not HSP27 content, correlated positively with cell survival. To separate the effects of organic osmolytes and HSP72, chronically NaCl-adapted MDCK cells were returned to isotonic medium for 1 or 2 days, so depleting them of trimethylamine osmolytes. HSP72, with its longer half life, remained elevated. Subsequent exposure of these cells to 600 mM urea in the medium resulted in about 80% survival. These results suggest that in MDCK cells and probably in the renal medulla, HSP72 and perhaps additional protective factors contribute substantially to the resistance against high urea concentrations.

Sodium ions absorbed from the intestine are postulated to act on the liver to reflexly suppress renal sympathetic nerve activity (RSNA), resulting in inhibition of sodium reabsorption in the kidney. To test the hypothesis that the renal sympathoinhibitory response to portal venous NaCl infusion involves an action of arginine vasopressin (AVP) at the area postrema, we examined the effects of portal venous infusion of hypertonic NaCl on RSNA before and after lesioning of the area postrema (APL) or after pretreatment with an AVP V1 receptor antagonist (AVPX). Rabbits were chronically instrumented with portal and femoral venous catheters, femoral arterial catheters, and renal nerve electrodes. Portal venous infusion of 9.0% NaCl (0.02, 0.05, 0.10, and 0.15 ml.kg-1.min-1 of 9.0% NaCl for 10 min) produced a dose-dependent suppression of RSNA (-12 +/- 3, -34 +/- 3, -62 +/- 5, and 80 +/- 2%, respectively) that was greater than that produced by femoral vein infusion of 9.0% NaCl (2 +/- 3, -3 +/- 2, -12 +/- 4, and -33 +/- 3%, respectively). The suppression of RSNA produced by portal vein infusion of 9.0% NaCl was partially reversed by pretreatment with AVPX (-9 +/- 3, -20 +/- 3, -41 +/- 4, and -55 +/- 4%, respectively) and by APL (-11 +/- 2, -25 +/- 2, -49 +/- 3, and -59 +/- 6%, respectively). There were no significant differences between the effects of AVPX and APL, and the effect of APL was not augmented by AVPX. These results indicate that the suppression of RSNA due to portal venous infusion of 9.0% NaCl involves an action of AVP via the area postrema.

In Wistar Kyoto (WKY) and Sprague Dawley rats, high dietary sodium chloride (NaCl) increases natriuretic and diuretic responses to acute isotonic saline infusion, but in NaCl-sensitive spontaneously hypertensive rats (SHR-S), a high-NaCl diet causes negligible increases in natriuretic and diuretic responses. To investigate whether this deficit in sodium and fluid excretion in SHR-S is stimulus (volume)-specific or because of a more generalized alteration in renal function, the present study measured, in SHR-S and Wistar Kyoto rats, natriuretic and diuretic responses to a hypertonic saline infusion (the amount of sodium infused was equal to that infused in a previous, isotonic experiment). Eight-week-old Wistar Kyoto rats, SHR-S, and salt-resistant SHR were given a basal (1%) or high (8%)-NaCl diet for 2 weeks. Intravenous infusion of hypertonic saline increased mean arterial pressure and reduced heart rate in all groups. Baseline sodium excretion was lower in SHR-S compared with salt-resistant SHR with either diet, but after infusion of hypertonic saline, all 6 groups displayed significant increases in sodium and fluid excretion, glomerular filtration rate, and effective renal blood flow (ERBF). The percent-sodium excretion in response to hypertonic saline infusion was slightly, but significantly, lower in SHR-S (compared with salt-resistant SHR) for either the basal or the high-NaCl diet. We conclude that renal responses to hypertonic saline infusion are affected minimally in SHR-S compared with salt-resistant SHR or Wistar Kyoto rats. Therefore, the deficits in renal function observed in SHR-S after volume loading are not reflected in a renal deficit to hypertonic saline challenge.

The neural mechanisms for pressor effects after hypertonic saline infusion are still unclear. Using direct measurement of the renal sympathetic nerve activity (RNA), we tested the hypothesis that the autonomic nervous system is involved in an acute blood pressure elevation produced by hypertonic saline (HTS) in anesthetized rabbits subjected to hemorrhage. Twenty urethane-anesthetized rabbits were ventilated mechanically after a tracheostomy and paralyzed with gallamine triethiodide. Heart rate (HR), mean blood pressure (MBP) and central venous pressure (CVP) were measured simultaneously with RNA. The animals were divided into the following four groups: (1) animals with intact baroreceptors that received HTS (intact HTS group, N = 5); (2) those with intact baroreceptors that received normal saline (intact NS group, N = 5); (3) those that underwent selective cervical vagotomy (vagotomy group, N = 5); (4) those with sino-aortic denervation (SAD group, N = 5). The last two groups were given HTS only. After inducing hemorrhagic hypotension to 40 mmHg over 10 min, 3.5% HTS at half the volume of shed blood was infused over approximately 120 s. In the intact HTS group, sympathetic activation, associated with tachycardia and pressor effects, developed. This enhancement of RNA was followed by a return to the pre-infusion level, but the increased blood pressure and tachycardia lasted until the end of the experiment. These levels of MBP and HR were significantly higher than those of the intact NS group. In the vagotomized animals, HTS resuscitation also increased RNA and systemic blood pressure. In contrast, in the SAD group, neither sympathetic activation nor an early phase increase in systemic blood pressure occurred. These results indicate that in hemorrhaged rabbits, 3.5% HTS produces sympathetic activation along with an acute pressor effect and that this is likely to be mediated through the sino-aortic nerves, possibly the peripheral chemoreceptors, but not through the vagal nerves.

1. Afferent nerve fibres sensitive to changes in the renal chemical environment have been found in the rat. To verify the existence of these fibres in the rabbit and their response pattern, afferent renal nerve activity was recorded during pelvic perfusions with NaCl solutions at different concentrations. 2. The experiments were carried out in 13 anaesthetized rabbits. Arterial pressure from a femoral catheter and afferent renal nerve activity from the distal stump of a cut renal nerve bundle were recorded. Three catheters were inserted into the renal pelvis to measure pelvic pressure, to allow pelvic perfusions at constant rates and to drain pelvic fluids. 3. After a control period, the pelvis was perfused with physiological saline (0.14 mol/l for 2 min), followed by one of a series of solutions containing increasing concentrations of NaCl (0.5, 0.75, 1.0 and 1.5 mol/l for 2 min). Pelvic perfusion was performed both at a low (0.2 ml/min) and a high (0.8 ml/min) flow rate for each solution tested. 4. In all animals arterial pressure was not modified during pelvic perfusions. Physiological saline did not change afferent renal nerve activity at the low perfusion rate, but it significantly increased afferent renal nerve activity and pelvic pressure at the high rate. Hypertonic NaCl solutions caused progressive increases in afferent renal nerve activity at both perfusion rates, and these effects were larger at the high perfusion rate. 5. These data demonstrate, in the rabbit, the existence of renal afferent nerves sensitive to discrete changes in pelvic ionic or osmotic concentration. The neural response is enhanced when renal mechano- and chemo-receptors are simultaneously activated.

The renal sympathetic responses to infusion of hypertonic solutions into the lateral cerebral ventricles were investigated in conscious sheep. Intracerebroventricular infusion of artificial cerebrospinal fluid (CSF) containing 0.6 M NaCl, at 1 ml/h for 20 min, reduced renal sympathetic nerve activity (RSNA) by 81 +/- 5% (n = 6, P < 0.001). Plasma renin concentration also fell (P < 0.05), whereas arterial pressure increased by 6.4 +/- 0.7 mmHg (P < 0.01). Intracerebroventricular hypertonic sorbitol (0.9 M in CSF at 1 ml/h) had no effect. The AT1 receptor antagonist losartan (1 mg/h) abolished the plasma renin and arterial pressure responses to intracerebroventricular hypertonic saline and significantly reduced the fall in RSNA to 17 +/- 10% (P < 0.001). During intracerebroventricular hypertonic saline, the baroreflex relation of RSNA to diastolic pressure was shifted to the left and that to central venous pressure was abolished compared with control relations obtained by manipulating pressure with intravenous phenylephrine. These findings indicate that 1) RSNA is inhibited by a central mechanism that senses high sodium (or perhaps chloride) concentration rather than hypertonicity; 2) this inhibition occurs independently of reflexes from high- and low-pressure baroreceptors, although these may enhance the inhibition; and 3) inhibition of RSNA by hypertonic saline involves a central angiotensinergic pathway.

The present study was carried out to study the effects of renal dopamine receptor blockade on natriuresis induced by volume expansion (VE) and intracerebroventricular injection of hypertonic saline (ICHNa) in connexion with the use of dopamine receptor blockers haloperidol (Hal) in anesthetized rabbits. In the VE experiments, Hal group decreases the peak increase of UNa V from control group of 65.0 +/- 15.0 to 19.0 +/- 5.5 mumol/min (P < 0.02). In the ICHNa experiments, the peak increase of UNa V in control and Hal groups were respectively 28.9 +/- 4.6 and 29.0 +/- 5.8 mumol/min (P > 0.50). In the experiments of rabbit with intact renal dopamine receptor, the natriuresis induced by VE+ICHNa was significantly greater than those due to either inducing factor acting alone. Renal dopamine receptor blockade also significantly attenuated the natriuresis induced by VE+ICHNa. These results indicate that renal dopamine receptor blockade significantly attenuated the natriuresis induced by VE or VE+ICHNa, but did not affect the response of ICHNa. In the rabbits with intact renal dopamine receptor, the natriuretic response induced by VE+ICHNa was significantly greater than those response by either inducing factor acting alone.

Neonatal capsaicin treatment has been reported to impair the excretory function of the kidney in the rat. The present study evaluated the effect on urine excretion of the neurotoxin resiniferatoxin, an extremely potent structural analogue of capsaicin. Neonatal resiniferatoxin treatment (30 micrograms/kg) markedly reduced diuresis, natriuresis and kaliuresis in adult rats, in response to intragastric saline or water load and to furosemide administration, as well as in basal conditions. The effect of resiniferatoxin was more pronounced and long-lasting than that observed in previous studies following neonatal capsaicin treatment (50 mg/kg). On the other hand, administration of resiniferatoxin in adult rats did not affect urine excretion, suggesting that afferent fibers resistant to the neurotoxin treatment during adulthood, might be involved in the effect. The results of the present study are in keeping with the hypothesis that neuropeptides-containing capsaicin-sensitive sensory neurons might be involved in the physiological modulation of the kidney function.

ET release by the renal epithelial Madin-Darby canine kidney (MDCK) cell line was investigated under isosmotic (300 mosmol/kg H2O; pH 7.4) and hyperosmotic (400, 500, or 600 mosmol/kg H2O) culture and assay conditions by the use of a specific and sensitive RIA. During isosmotic incubation, MDCK cells, which may be of collecting duct origin, secreted by far more ET into the cell culture supernatant (495.7 +/- 25.5 fmol.mg of protein-1.24 h-1) than did the proximal tubule-derived LLC-PK1 (2.42 +/- 0.20 fmol.mg of protein-1.24 h-1) and opossum kidney (3.12 +/- 0.47 fmol.mg of protein-1.24 h-1) cells. ET secretion by MDCK monolayers increased progressively within 24 h and then only slightly declined up to 48 h. Phosphoramidon (100 mumol/L) inhibited the constitutive ET synthesis in MDCK cells by 60%, indicating the participation of a phosphoramidon-sensitive ET-converting enzyme in the processing of bigET to ET in these cells. MDCK epithelia grown on filter inserts showed a clear polarity in their ET release. The baseline secretion of ET was 2.5 times higher to the basolateral than to the apical side, which might be in support of a predominantly basolateral action of the peptide. Short-term incubation of MDCK cells in hyperosmotic NaCl media for 24 h dose dependently decreased ET production. When urea was used as the solute to generate hyperosmolality, ET release by MDCK cells significantly increased. In contrast, when raffinose was added to increase osmolality to 500 mosmol/kg H2O, a decrease of ET production in a range similar to the effect of NaCl was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Our previous studies have shown that stimulation of the anteroventral third ventricle (AV3V) region of the brain increases atrial natriuretic peptide (ANP) release, whereas lesions of the AV3V region or median eminence of the tuber cinereum block the release of ANP caused by blood volume expansion. These results suggest that participation of the central nervous system is critical to this response. The role of baroreceptors in the response was evaluated in the current research by studying the response of plasma ANP to blood volume expansion induced by intravenous injection of hypertonic saline solution (0.3 M NaCl, 2 ml/100 g of body weight, over 1 min) in conscious, freely moving male rats. Plasma samples were assayed for ANP by radioimmunoassay. In sham-operated rats, blood volume expansion induced a rapid increase in plasma ANP: the concentration peaked at 5 min and remained elevated at 15 min after saline injection. One week after deafferentation of the carotid-aortic baroreceptors, basal plasma ANP concentrations were highly significantly decreased on comparison with values of sham-operated rats; plasma ANP levels 5 min after blood volume expansion in the deafferented rats were greatly reduced. Unilateral right vagotomy reduced resting levels of plasma ANP but not the response to blood volume expansion; resting concentrations of plasma ANP and responses to expansion were normal in bilaterally vagotomized rats. In rats that had undergone renal deafferentation, resting levels of ANP were normal but the response to blood volume expansion was significantly suppressed. The evidence indicates that afferent impulses via the right vagus nerve may be important under basal conditions, but they are not required for the ANP release induced by blood volume expansion. In contrast, baroreceptor impulses from the carotid-aortic sinus regions and the kidney are important pathways involved in the neuroendocrine control of ANP release. The evidence from these experiments and our previous stimulation and lesion studies indicates that the ANP release in response to volume expansion is mediated by afferent baroreceptor input to the AV3V region, which mediates the increased ANP release via activation of the hypothalamic ANP neuronal system.

This study evaluates the effects of methimazole, an antithyroid drug, on blood pressure, digoxin-like immunoreactive factor (DLIF) production and other variables related to salt and water metabolism in low-renal mass (LRM) hypertension. Drinking administration of methimazole (0.025%) from replacement of water by the 1% NaCl solution maintained the blood pressure of low-renal mass rats at normal levels during four weeks after hypertension induction. Serum and urinary excretion of DLIF were significantly increased in LRM rats with respect to controls; in all tests, the highest values of DLIF were found in LRM-methimazole treated (LRM-M) rats. Urinary excretion of DLIF showed positive correlations with diuresis and natriuresis in all three groups (control, LRM and LRM-M rats). However, the correlation between DLIF and sodium disappeared when both factors were expressed as a function of their concentrations. These results indicate that methimazole prevents LRM hypertension and suggest that DLIF might not represent the putative natriuretic hormone. Other findings were that methimazole-treatment reduced renal compensatory hypertrophy subsequent to subtotal nephrectomy, and did not modify the characteristic polyuria-polydypsia in this type of hypertension.

Domestic ducks adapted to saline of 400 mosmol/kgH2O as their only water supply received intravenous loads of 100 mM KCl for 2 h while being intravenously infused with 200 mM NaCl at 1.0 ml/min to produce simultaneous salt gland secretion and diuresis-natriuresis. K+ loading did not alter the plasma levels of the osmoregulatory hormones arginine vasotocin, angiotensin II, aldosterone, and atrial natriuretic factor but promptly evoked kaliuresis because of a rise from 17 to 155 mM in urinary K+, with a proportional decrease in urinary Na+. Continuous infusion of amiloride (0.04 mg.min.-1.kg body wt-1 iv) further enhanced diuresis and natriuresis and lowered urinary K+, but the kaliuretic response to K+ loading was only moderately reduced because of enhanced diuresis and a rise in urinary K+ from 3 to 33 mM, with a slight decrease in urinary Na+. Changes in plasma hormone levels reflected dehydration due to excessive diuresis but were not related to kaliuresis. Salt gland secretion was not affected directly by amiloride but was secondarily reduced by the induced dehydration. In amiloride-treated ducks, hyperkalemia in response to K+ loading was exaggerated relative to the modest reduction in K+ excretion and may be attributed to moderate metabolic acidosis and/or general effects of amiloride on K+ metabolism. It is concluded that none of the established osmoregulatory hormones is involved in short-term control of renal K+ handling in ducks and that distal tubular K+ excretion involving amiloride-sensitive Na+ channels is quantitatively unimportant in this avian species.

The effects of brain natriuretic peptide (BNP) on renin secretion were evaluated in normal and hypertonic saline-infused kidneys of anesthetized dogs. In the normal kidney (N = 5), intrarenal infusion of porcine BNP-(1-26) (pBNP) at a dose of 50 ng/kg per min attenuated the renin secretion rate significantly to 9 +/- 27% of control without exerting a significant effect on mean arterial pressure (MAP), renal blood flow (RBF) or glomerular filtration rate (GFR); urine flow (V) was significantly increased to 260 +/- 33% of control and urinary excretion of sodium (UNaV) to 480 +/- 140% of control. In the hypertonic saline infusion group (N = 6), intrarenal infusion of hypertonic saline (20% w/v) at 0.5, 0.8, and 1.0 mEq NaCl/min caused a decrease in GFR and natriuresis in a dose-dependent manner. The renin secretion rate was attenuated by hypertonic saline infusion (1 mEq NaCl/min) to 87 +/- 31% of control. In another group (N = 6), administration of pBNP at a dose of 50 ng/kg per min during hypertonic saline infusion (1 mEq NaCl/min) increased the renin secretion rate to 196 +/- 57%, increased RBF to 160 +/- 13%, increased GFR to 137 +/- 22%, increased V to 221 +/- 29%, and increased UNaV to 218 +/- 29% of the values measured during hypertonic saline infusion. Our results indicate that BNP inhibits renin secretion through sodium delivery to the macula densa and effectively inhibits the tubuloglomerular feedback response that is activated by intrarenal hypertonic saline infusion.

The anterodorsal part of the third ventricle of conscious ducks was perfused intracerebroventricularly (icv) for 10 min with norepinephrine (NE) or with its agonists phenylephrine (alpha 1, Phe), isoproterenol (beta, Iso), and clonidine (alpha 2, Clo) in artificial CSF (aCSF). Their effects on the plasma level of antidiuretic hormone (AVT, arginine vasotocin in birds), urine excretion, heart rate (HR), and mean arterial pressure (MAP) were investigated in steady-state water diuresis. The correct position of the icv cannula was confirmed by enhanced AVT release and antidiuresis in response to icv perfusion of aCSF made hypertonic (400 mosmol/kgH2O) by adding NaCl. Icv perfusion with hypertonic aCSF and 750 ng/min NE had comparable effects on AVT release and urine excretion, but hypertonic aCSF caused small increases in MAP and HR, whereas NE depressed both MAP and HR. Antidiuresis and circulatory depression caused by NE icv perfusion was dose dependent. Among the adrenergic agonists perfused at similar doses (188 ng/min), only Iso stimulated AVT release. Iso and Phe had small depressive effects on MAP and HR (less than 10%). Clo depressed circulation by greater than 20% for longer than 60 min, and AVT release became significantly reduced 30 min after the start of icv perfusion. The consistent results in ducks contrast with the equivocal data hitherto reported for central stimulations with NE or its agonists in mammals and may be due to the concentric perfusion system used in our study for localized stimulations in the vicinity of the paraventricular nucleus.

The observation that electrical stimulation of the renal nerves increases vasopressin secretion raises the possibility that the renal nerves may participate in the control of vasopressin secretion. In the present investigation, the effects of renal denervation on the vasopressin response to two reflex stimuli (nitroprusside infusion and hemorrhage) and two osmotic stimuli (hypertonic saline infusion and water deprivation) were studied in conscious, chronically prepared rabbits. Nitroprusside infusion in 13 intact and 14 denervated rabbits caused similar decreases in mean arterial pressure (MAP) and the increase in plasma arginine vasopressin concentration (PAVP) in intact (2.6 +/- 0.3 to 5.8 +/- 0.9 pg/ml, P less than 0.01) and denervated (2.8 +/- 0.3 to 5.7 +/- 1.3 pg/ml, P less than 0.01) rabbits was not significantly different. Hemorrhage (20 ml/kg) in 15 intact and 14 denervated rabbits caused similar decreases in MAP. Again, the increase in PAVP from 2.7 +/- 0.3 to 159.0 +/- 37.1 pg/ml (P less than 0.01) in intact and from 5.0 +/- 1.7 to 115.4 +/- 45.6 pg/ml (P less than 0.01) in denervated rabbits was not significantly different, nor was the relationship between PAVP and MAP in the two groups. In seven intact rabbits, hypertonic saline infusion increased PAVP from 4.0 +/- 0.9 to 10.9 +/- 2.8 pg/ml (P less than 0.05). The change in six denervated rabbits was not significantly different, nor was the relationship between PAVP and plasma osmolality. During water deprivation (24 h) in six intact rabbits, PAVP increased from 4.0 +/- 0.7 to 6.9 +/- 0.6 pg/ml (P less than 0.05). Again, the increase in PAVP in six denervated rabbits was not significantly different from that in the intact rabbits. The change in MAP during water deprivation in the two groups was also not significantly different. Renal cortical norepinephrine concentration in denervated kidneys was less than 10 ng/g wet wt. These results indicate that, in conscious rabbits, renal denervation does not impair the osmotic or reflex regulation of vasopressin secretion, nor does it interfere with blood pressure regulation during hypovolemia or hypotension.

Intrarenal artery infusion of hypertonic saline induces a sustained renal vasoconstriction that is most likely mediated by tubuloglomerular feedback. The purpose of this study was to investigate the contribution of angiotensin II and adenosine to this response in normal-salt and salt-deplete states. Intrarenal infusions of hypertonic saline to sodium-deplete dogs caused a renal vaso-constrictor response that was observed between 5 and 10 min into the infusion. This response was attenuated in dogs on a normal-salt diet and in salt-deplete dogs receiving captopril. Intravenous infusion of subpressor doses of angiotensin II to dogs either on a normal-salt intake or on a salt-deplete diet but receiving captopril, restored the vasoconstrictor response to hypertonic saline. The vasoconstrictor response in the presence of an angiotensin II infusion in each of these two groups of dogs was abolished by an intrarenal artery infusion of the adenosine receptor blocker, theophylline. These experiments are consistent with the hypothesis that intrarenal infusion of hypertonic saline enhances the endogenous production of adenosine and that the ability of adenosine to reduce renal blood flow is dependent on the presence of angiotensin II.

The change in renal nerve activity under conditions known to increase renal sodium excretion was studied. In adult Sprague Dawley rats, anaesthetized with Inactin, normotonic and hypertonic NaCl solutions were infused into 1) a vein, 2) a carotid artery and 3) the third ventricle. The left kidney was freed and placed in a plastic cup. A renal nerve was dissected free and placed on a stainless bipolar electrode. The nerve was cut distal to the electrode. The nerve signals were amplified and recorded on a tape recorder. Simultaneously integrated nerve signals and also atrial and venous pressures were recorded. Intracarotid infusion of a 1 M NaCl solution increased sodium output and temporarily decreased renal nerve activity by some 35%. Corresponding intravenous (i.v.) infusion gave an increase in renal nerve activity and also in sodium output. The latter increase was delayed compared with that caused by the intracarotid infusion. No variations in blood pressure were noted. In control experiments with a slow i.v. infusion of physiological saline, renal nerve activity increased throughout the experiment, while sodium excretion remained constant. During infusion of a 1 M NaCl solution into the third ventricle, renal nerve activity decreased in about half of the cases. This reduction was often accompanied by an increased arterial blood pressure and an increased sodium output. Arterial blood pressure increases were especially pronounced at the highest infusion rats, i.e. 800 ml-min-1. Isotonic volume expansion of 2% of the body weight resulted in a transient decrease in renal nerve activity by about 30%. Venous blood pressure rose and sodium output increased six-fold. The decrease in nerve activity was observed both when the vagal nerves were intact and when they were cut.

The avian kidney has a dual blood supply: one arising from the renal arteries and the other from the renal portal system. In anesthetized pullets (Gallus gallus) two major shunt pathways bypassing the kidney were occluded to ensure the venous blood returning from the leg suffuses the peritubular sites before it enters the systemic circulation. Urine was collected from the ureteral orifices. When 5% NaCl (2.0 ml X kg-1 X h-1) was infused for 20 min into the renal portal system, urine flow and urinary NaCl concentrations and excretion rates increased immediately in the infused side. Infusion of 5% NaCl into the systemic circulation produced no natriuresis. Infusion of 10% NaCl (4.0 ml X kg-1 X h-1), into either the systemic or renal portal route, caused a prolonged antidiuresis. Plasma renin activity (PRA) decreased after portal infusion of 5% NaCl and after both portal and systemic infusion of 10% NaCl. These results suggest that 1) infusion of hypertonic saline into the renal portal system produces local renal effects and 2) increases in tubular or peritubular NaCl levels may suppress PRA.

During saline infusion, sodium reabsorption (RNa) in the diluting segment (thick ascending limb of Henle's loop) increases acutely. The mechanism for this higher pumping rate of outer medullary Na-K-ATPase is unknown. Following left-sided nephrectomy, immediate i.v. infusion of hypertonic saline increased RNa in the remaining whole right kidney by 28 +/- 14% (p less than 0.05). Na-K-ATPase activity in outer medulla was raised by (delta) 23 +/- 4% above the left kidney (p less than 0.05), whereas cortical activity was unchanged. The mechanism for this increase in Na-K-ATPase activity was explored. The catalytic rate per enzyme did not differ in the two kidneys and equalled 5 340 min-1. The increase was therefore due to higher tissue concentration of active enzyme. The response was fully developed during continuous infusion within 20 min, and of equal magnitude whether protein synthesis had been inhibited by cycloheximide (delta = 23 +/- 7%) or stimulated by unilateral nephrectomy 6 days earlier combined with saline infusion for 2 h (delta = 34 +/- 10%). Thus, during hypertonic saline infusion, the increased RNa in the outer medulla was partly accounted for by the activation of latent Na-K-ATPase. High delivery of sodium to the diluting segment for more than 20 min during hypertrophy caused no further activity change.

1. The influence of partial hepatectomy on urinary concentrating ability and renal tissue sodium was determined in conscious rats deprived of water for 24 h. In comparison with a sham operation, partial hepatectomy resulted in: a) a 50% reduction in free-water reabsorption, urinary osmolality, and osmolal urine-to-plasma ratio; b) depression of free-water reabsorption at similar levels of osmolal clearance above 200 microliter/min per ml of GFR during the infusion of hypertonic NaCl and vasopressin; and c) a 30% reduction in sodium content of the renal papilla and outer medulla. 2. The renal response to an intravenous water load (2.5% glucose infused to 2.5% of body wt at 0.4 ml/min) was determined in sham-operated and partially hepatectomized, conscious rats. By 60 min after the water load, both groups had excreted practically all of the load. However, during and for 30 min after the infusion in the partially hepatectomized group, the percent of the water load excreted, urine flow, and free-water clearance were significantly reduced while urinary osmolality and osmolal urine-to-plasma ratio were significantly elevated. 3. These experiments demonstrate that shortly after partial removal of the liver the renal concentrating ability is defective and the excretion of a water load is not grossly impaired.

Verney's hypothesis of cerebral osmoreceptors controlling the renal excretion of water via vasopressin was reinvestigated in conscious trained dogs provided with bilateral skin loops containing the common carotid arteries. In multiple experiments in two dogs, bilateral intracarotid injections (0.25 ml. (kg b.wt.)-1 per artery in 10 s) of a hyperosmotic solution of sodium chloride (0.257 mol/l) during transient water diuresis failed to produce an antidiuretic response, although it is estimated that the injections elevated the osmolality of the carotid blood by 12-15%. In another 5 dogs, Bilateral intracarotid infusions of hyperosmotic saline (45 mumol.(kg b wt..min)-1 per artery for 10 min) during sustained water diuresis resulted in a 3% increase in jugular venous osmolality and an antidiuretic response without detectable changes in heart rate or mean arterial pressure. Equal intravenous hyperosmotic or intracarotid isosmotic infusions were not associated with antidiuretic response. Analysis of the concomitant concentrations of vasopressin in plasma fell short of supporting the hypothesis that the antidiuretic response to intracarotid hyperosmotic infusions was exclusively or mainly due to liberation of vasopressin, although the renal response could be mimicked by exogenous vasopressin. It is concluded that the present results-although discordant with several of Verney's results and assumptions-nevertheless support the concept of a cerebral solute receptor influencing the rate of renal water excretion.

To examine potential mechanisms responsible for the greater prevalence of hypertension among relatives of hypertensives than among relatives of normotensives, we subjected 43 normotensive first-degree relatives of known essential hypertensives and 43 age-, race-, and sex-matched normal subjects with no family history of hypertension to sodium loading and depletion. The data show that the relatives had higher blood pressures than did controls. They also had higher PRA values before and after a 2 L intravenous saline infusion over 4 hr. In addition, the relatives excreted less (p less than 0.05) sodium on the day of the infusion than did the controls. PA values and UNe excretion in the two groups did not differ. In the relatives, age correlated with systolic and diastolic blood pressure. Age correlated inversely with the 24 h urine sodium excretion on the sodium loading day. These correlations were not observed in controls. Normotensive first-degree relatives of hypertensives differ from relatives of nonhypertensives in that they have higher PRA values and a blunted natriuretic response to a saline load. These features may predispose them to the development of hypertension.

The contribution of fetal urine to the increase in amniotic fluid osmolality during maternal hypertonicity was studied in chronically catheterized sheep of 130-135 days gestation. Nine percent NaCl was injected simultaneously into fetal and maternal veins, followed by a continuous infusion into the maternal vein. Maternal and fetal plasma osmolalities rose by 15 +/- 1 (SE) and 13 +/- 1 mosmol/kg, respectively, and remained constant for 4 h. Fetal urine osmolality rose significantly from 188 +/- 31 to 277 +/- 32 mosmol/kg within 1 h and remained constant thereafter. Fetal urine flow rose transiently, fell to normal within 10 min, and averaged 70% of normal beyond 1 h. Amniotic fluid osmolality rose by 10.8 +/- 2.8 mosmol/kg over 4 h. Following hypertonic injection into three fetuses blocked by the arginine vasopressin antagonist d(CH2)5D-tyr(Et)VAVP, urine osmolality did not change, and amniotic fluid osmolality rose by 2.7 +/- 0.3 mosmol/kg. Thus it appears that the increase in amniotic fluid osmolality during maternal hypertonicity may be due largely to an increased fetal urine osmolality coupled with a decreased flow of fetal urine into the amniotic space, rather than to bulk flow of fluid across the membranes and uterine wall.