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Efficient oxygen utilization in the kidney may be supported by paracellular epithelial transport, a form of passive diffusion that is driven by preexisting transepithelial electrochemical gradients. Claudins are tight-junction transmembrane proteins that act as paracellular ion channels in epithelial cells. In the proximal tubule (PT) of the kidney, claudin-2 mediates paracellular sodium reabsorption. Here, we used murine models to investigate the role of claudin-2 in maintaining energy efficiency in the kidney. We found that claudin-2-null mice conserve sodium to the same extent as WT mice, even during profound dietary sodium depletion, as a result of the upregulation of transcellular Na-K-2Cl transport activity in the thick ascending limb of Henle. We hypothesized that shifting sodium transport to transcellular pathways would lead to increased whole-kidney oxygen consumption. Indeed, compared with control animals, oxygen consumption in the kidneys of claudin-2-null mice was markedly increased, resulting in medullary hypoxia. Furthermore, tubular injury in kidneys subjected to bilateral renal ischemiareperfusion injury was more severe in the absence of claudin-2. Our results indicate that paracellular transport in the PT is required for efficient utilization of oxygen in the service of sodium transport. We speculate that paracellular permeability may have evolved as a general strategy in epithelial tissues to maximize energy efficiency., Introduction Epithelia are sheets of cells that separate body compartments of different compositions and function as physical and chemical barriers. For almost a century, it was believed that epithelial cells [...]

Adenosine can mediate the tubuloglomerular (TGF) response via activation of [A.sub.1] receptors on the afferent arteriole, but both adenosine [A.sub.1] and [A.sub.2] receptors can regulate preglomerular resistance. We tested the hypothesis that adenosine [A.sub.2] receptors offset the effect of [A.sub.1] receptors and modulate the TGF. Maximal TGF responses were measured in male Sprague-Dawley rats as changes in proximal stop-flow pressure ([DELTA][P.sub.SF]) in response to increased perfusion of the loop of Henle (0 to 40 nl/min) with artificial tubular fluid (ATF). The maximal TGF response was studied after 5 rain of intratubular perfusion (10 nl/min) with ATF alone, or with ATF plus the [A.sub.2A] receptor antagonist (ZM-241385; [10.sup.-7] or [10.sup.-5] tool/l), [A.sub.1] receptor antagonist (PSB-36; [10.sup.-8] mol/l), or with a combination of [A.sub.1] (PSB-36; [10.sup.-8] mol/l) and [A.sub.2A] (ZM-241385; [10.sup.-7] mol/1) antagonists. The maximal TGF response ([DELTA][P.sub.SF]) with ATF alone was 11.7 [+ or -] 1.0 mmHg. Specific [A.sub.2] inhibition (low dose) enhanced the maximal TGF response (15.7 [+ or -] 0.8 mmHg; P < 0.01), whereas a high dose (unspecific inhibition) attenuated the response (5.0 [+ or -] 0.4 mmHg; P < 0.001). [A.sub.1] inhibition alone led to a paradoxical TGF response, with an increase in [P.sub.SF] of 3.1 [+ or -] 0.5 mmHg (P < 0.05). Simultaneous application of [A.sub.1] and [A.sub.2] antagonists abolished the TGF response ([DELTA][P..sub.SF]: 0.4 [+ or -] 0.3 mmHg). In conclusion, adenosine [A.sub.2] receptors modulate the TGF response by counteracting the effects of adenosine [A.sub.1] receptors. adenosine receptors; kidney; micropuncture; renal microcirculation doi: 10.1152/ajprenal.00211.2010.

Araujo M, Welch WJ. Tubuloglomerular feedback is decreased in COX-1 knockout mice after chronic angiotensin II infusion. Am J Physiol Renal Physiol 298: F1059-F1063, 2010. First published January 27, 2010; doi: 10.1152/ajprenal.00547.2009.--Prostaglandins (PGs), produced by two isoforms of cyclooxygenase (COX), COX-1 and COX-2, are important modulators of renal hemodynamics. COX-1 and COX-2 are expressed in the kidney often at distinct sites. Thromboxane ([TxA.sub.2]), [PGE.sub.2], and prostacyclin (PGI2) are the major PGs in the renal cortex of mice. Acute infusion of the vasoconstrictor ANG II increases COX-2-dependent [PGE.sub.2] and [PGI.sub.2]. COX-2 is primarily expressed in the macula densa (MD), where several PG synthases are also expressed. We previously showed that MD COX-2 products modulate tubuloglomerular feedback (TGF) in the rat. Genetic deletion of COX-1 enhances COX-2 production of PGs, decreases renal and urinary PGs, and attenuates ANG II-induced hypertension. The present study tested the effects of chronic ANG II infusion on TGF in COX-1 knockout (KO) mice. Basal TGF was similar in COX-1 KO and wild-type (WT) mice. Chronic ANG II infusion increased TGF in WT mice (WT: 9.3 [+ or -] 0.7 vs. WT + ANG II: 12.2 [+ or -] 1.6 mmHg, P < 0.02). However, chronic ANG II decreased TGF in COX-1 KO mice (KO: 11.4 [+ or -] 1.1 vs. KO + ANG II: 8.3 [+ or -] 0.6 mmhg, P < 0.01). Pretreatment with the COX-2 inhibitor SC58,236 in COX-1 KO mice prevented the ANG II-associated reduction in TGF (11.4 [+ or -] 1.0 vs. 11.5 [+ or -] 0.28 mmHg, not significant). Excretion of 6-keto-[PGF.sub.2[alpha]], the metabolite of PGI2, was increased by ANG II infusion, whereas excretion of TxB2, the stable metabolite of [TxA.sub.2], was not changed. ANG II infusion increased mean arterial pressure similarly in both WT and KO mice (WT: 93 [+ or -] 2 vs. KO: 92 [+ or -] 3 mmHg), but not in KO mice pretreated with SC-58,236 (85 [+ or -] 2 mmHg). This study shows that COX-l-generated PGs partially mediate ANG II increases in TGF and that COX-2 PGs offset that effect. cyclooxygenase; prostaglandins; hypertension doi: 10.1152/ajprenal.00547.2009.

Thromboxane (Tx[A.sub.2]) and nitric oxide (NO) are potent vasoactive autocoids that modulate tubuloglomerular feedback (TGF). Each is produced in the macula densa (MD) by cyclooxygenase-2 (COX-2) and neuronal nitric oxide synthase (nNOS), respectively. Both enzymes are similarly regulated in the MD and their interaction may be an important factor in the regulation of TGF and glomerular filtration rate. We tested the hypothesis that TGF is modified by the balance between MD nNOS-dependent NO and MD COX-2-dependent Tx[A.sub.2]. We measured maximal TGF during perfusion of the loop of Henle (LH) by continuous recording of the proximal tubule stopped flow pressure response to LH perfusion of artificial tubular fluid (ATF) at 0 and 40 nl/min. The response to inhibitors of COX-1 (SC-560), COX-2 [parecoxib (Pxb)], and nNOS (L-NPA) added to the ATF solution was measured in separate nephrons. COX-2 inhibition with Pxb reduced TGF by 46% (ATF + vehicle vs. ATF + Pxb), whereas COX-1 inhibition with SC-560 reduced TGF by only 23%. Pretreatment with intravenous infusion of SQ-29,548, a selective thromboxone/PGH2 receptor (TPR) antagonist, blocked all of the SC-560 effect on TGF, suggesting that this effect was due to activation of TPR. However, SQ-29,548 only partially diminished the effect of Pxb (-66%). Specific inhibition of nNOS with L-NPA increased TGF, as expected. However, the ability of Pxb to reduce TGF was significantly impaired with comicroperfusion of L-NPA. These data suggest that COX-2 modulates TGF by two proconstrictive actions: generation of Tx[A.sub.2] acting on TPR and by simultaneous reduction of NO. blood flow; systemic volume; electrolyte homeostasis

Adenosine mediates [Na.sup.+] reabsorption in the proximal tubule (PT) and other segments by activating adenosine type 1 receptors (A1-AR). We tested the hypothesis that A1-AR in the PT is regulated by salt intake and participates in the kidney adaptation to changes in salt intake. Absolute fluid reabsorption ([J.sub.v]) was measured by direct in vivo microperfusion and recollection in rats maintained on low (LS; 0.03% Na, wt/wt)-, normal (NS; 0.3% Na)-, and high-salt (HS; 3.0% Na) diets for 1 wk. The effect of microperfusion of BG9719 a highly selective inhibitor of A1-ARs or adenosine deaminase (AD), which metabolizes adenosine, was measured in each group. [J.sub.v] was higher in PT from LS rats (LA: 2.8 [+ or -] 0.2 vs. NS: 2.1 [+ or -] 0.2 nl * [min.sup.-1] * [mm.sup.-1], P < 0.001). [J.sub.v] in HS rats was not different from NS. BG9719 reduced [J.sub.v] in LS rats by 66 [+ or -] 6% (LS: 2.8 [+ or -] 0.2 vs LS+CVT: 1.3 [+ or -] 0.3 nl * min.sup.-1] * [mm.sup.-1], p < 0.001), which was greater than its effect in NS (45 [+ or -] 4%) or HS (41 [+ or -] 4%) rats. AD reduced [J.sub.v] similarly, suggesting that A1-ARs are activated by local production of adenosine. Expression of A1-AR mRNA and protein was higher (P < 0.01) in microdissected PTs in LS rats compared with NS and HS. We conclude that A1-ARs in the PT are increased by low salt intake and that A1-AR participates in the increased PT reabsorption of solute and fluid in response to low salt intake. fluid reabsorption; microperfusion

Acute intravenous Tempol reduces mean arterial pressure (MAP) and heart rate (HR) in spontaneously hypertensive rats. We investigated the hypothesis that the antihypertensive action depends on generation of hydrogen peroxide, activation of heme oxygenase, glutathione peroxidase or potassium conductances, nitric oxide synthase, and/or the peripheral or central sympathetic nervous systems (SNSs). Tempol caused dose-dependent reductions in MAP and HR (at 174 [micro]mol/kg; [DELTA]MAP, -57 [+ or -] 3 mmHg; and [DELTA]HR, -50 [+ or -] 4 beats/min). The antihypertensive response was unaffected by the infusion of a pegylated catalase or by the inhibition of catalase with 3-aminotriazole, inhibition of glutathione peroxidase with buthionine sulfoximine, inhibition of heme oxygenase with tin potassium channels with iberiotoxin. However, the antihypertensive response was significantly (P < 0.01) blunted by 48% by the activation of adenosine 5'-triphosphate-sensitive potassium ([K.sub.ATP]) channels with cromakalim during maintenance of blood pressure with norepinephrine and by 31% by the blockade of these channels with glibenclamide, by 40% by the blockade of nitric oxide synthase with [N.sup.[omega]]-nitro-L-arginine methyl ester (L-NAME), and by 40% by the blockade of ganglionic autonomic neurotransmission with hexamethonium. L-NAME and hexamethonium were additive, but glibenclamide and hexamethonium were less than additive. The central administration of Tempol was ineffective. The acute antihypertensive action of Tempol depends on the independent effects of potentiation of nitric oxide and inhibition of the peripheral SNS that involves the activation of [K.sub.ATP] channels. superoxide dismutase; nitric oxide synthase; sympathetic nervous system; catalase; adenosine 5'-triphosphate-activated potassium channels

Angiotensin (ANG) II activating type 1 receptors (ATIRs) enhances superoxide anion ([O.sub.2.sup.*-]) and arachidonate (AA) formation. AA is metabolized by cyclooxygenases (COXs) to [PGH.sub.2], which is metabolized by thromboxane (Tx)[A.sub.2] synthase to Tx[A.sub.2] or oxidized to 8-isoprostane [PGF.sub.2[alpha]] (8-Iso) by [O.sub.*-]. [PGH.sub.2], Tx[A.sub.2], and 8-Iso activate thromboxane-prostanoid receptors (TPRs). We investigated whether blood pressure in a rat model of early (3 wk) two-kidney, one-clip (2K,1C) Goldblatt hypertension is maintained by [AT.sub.1]Rs or [AT.sub.2]Rs, driving COX-1 or -2-dependent products that activate TPRs. Compared with sham-operated rats, 2K,1C Goldblatt rats had increased mean arterial pressure (MAP; 120 [+ or -] 4 vs. 155 [+ or -] 3 mmHg; P < 0.001), plasma renin activity (PRA; 22 [+ or -] 7 vs. 48 [+ or -] 5 ng x [m1.sup.-1] x [h.sup.-l]; P < 0.01), plasma malondialdehyde (1.07 [+ or -] 0.05 vs. 1.58 [+ or -] 0.16 nmol/1; P < 0.01), and Tx[B.sub.2] excretion (26 [+ or -] 4 vs. 51 [+ or -] 7 ng/24 h; P < 0.01). Acute graded intravenous doses of benazeprilat (angiotensin-converting enzyme inhibitor) reduced MAP at 20 min (-36 [+ or -] 5 mmHg; P < 0.001) and excretion of Tx[A.sub.2] metabolites. Indomethacin (nonselective COX antagonist) or SC-560 (COX-1 antagonist) reduced MAP at 20 min (-25 [+ or -] 5 and -28 [+ or -] 7 mmHg; P < 0.001), whereas valdecoxib (COX-2 antagonist) was ineffective (-9 [+ or -] 5 mmHg; not significant). Losartan ([ATI.sub.1]R antagonist) or SQ-29548 (TPR antagonist) reduced MAP at 150 min (-24 [+ or -] 6 and -22 [+ or -] 3 mmHg; P < 0.001), whereas PD-123319 ([AT.sub.2]R antagonist) was ineffective. Acute blockade of TPRs, COX-1, or COX-2 did not change PRA, but Tx[B.sub.2] generation by the clipped kidney was reduced by blockade of COX-1 and increased by blockade of COX-2.2K, 1C hypertension in rats activates renin, [O.sub.2.sup*-], and vasoconstrictor PGs. Hypertension is maintained by [AT.sub.1]Rs and by COX-1, but not COX-2, products that activate TPRs. renovascular hypertension; angiotensin receptor blocker; thromboxane [A.sub.2]; isoprostane; angiotensin-converting enzyme inhibition

Angiotensin II (ANG II) infusion increases renal superoxide ([O.sup.-.sub.2]) and enhances renal vasoconstriction via macula densa (MD) regulation of tubuloglomerular feedback, but the mechanism is unclear. We targeted the [p22.sup.phox] subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) with small-interfering RNA (siRNA) to reduce NADPH oxidase activity and blood pressure response to ANG II in rats. We compared single nephron glomerular filtration rate (SNGFR) in samples collected from the proximal tubule (PT), which interrupts delivery to the MD, and from the distal tubule (DT), which maintains delivery to the MD, to assess MD regulation of GFR. SNGFR was measured in control and ANG II-infused rats (200 ngx[kg.sup.-1]x[min.suup.-1] for 7 days) 2 days after intravenous injection of vehicle or siRNA directed to [p22.sup.phox] to test the hypothesis that [p22.sup.phox] mediates MD regulation of SNGFR during ANG II. The regulation of SNGFR by MD, determined by PT SNGFR-DT SNGFR, was not altered by siRNA in control rats (control + vehicle, 13 [+ or -] 1, n = 8; control + siRNA, 12 [+ or -] 2 nl/min, n = 8; not significant) but was reduced by siRNA in ANG II-treated rats (ANG II + vehicle, 13 [+ or -] 2, n = 7; ANG II + siRNA, 7 [+ or -] 1 nl/min, n = 8; P < 0.05). We conclude that [p22.sup.phox] and NADPH oxidase regulate the SNGFR during ANG II infusion via MD-dependent mechanisms. renal function; oxidative stress; hypertension; tubuloglomerular feedback; glomerular filtration rate

The relationship between the stress protein response and the acute phase response (APPR) was studied in human hepatoma cells to investigate the hierarchy of regulation of these survival responses. Huh-7 cells were subjected to heat treatment (febrile-range temperature 40[degrees]C or heat shock 43[degrees]C) followed by recovery at 37[degrees]C in the presence or absence of IL-6 given either before or after heat treatment. The effects on total, fractional, and acute phase protein synthesis were then analyzed by metabolic labeling, ELISA, real-time PCR, Northern blot analysis, and activation of au [alpha].sub.1]-antitrypsin reporter plasmid. Cell energetics were studied under the same conditions using an index of mitochondrial activity and measurement of cellular ATP levels. Febrile-range temperature (40[degrees]C) augmented acute phase protein production when cells had been pretreated with IL-6. Pretreatment of cells with IL-6 also prevented heat shock-induced suppression of [[alpha].sub.1-antichymotrypsin (ACT) but not transferrin, mRNA expression of ACT and [[alpha].sub.1-antitrypsin reporter activation studies was consistent with transcriptional regulation of these proteins. Expression of mRNA transcripts for transferrin was increased despite protein expression being reduced by heat shock. The effects of heat shock on acute phase protein synthesis can be modified by preincubation with IL-6, whereas addition of this ligand after heat treatment has no effect on the suppressive effect of heat on the APPR. The mechanism of this action appears to be transcriptionally regulated in the case of ACT, but in the case of transferrin, it may be mediated by another process such as posttranslational modification. [[alpha].sub.1-antitrypsin: hepatocyte; acute phase protein; stress response; [[alpha].sub.1]-antichymotrypsin; transferrin

Tempol is an amphipathic radical nitroxide (N) that acutely reduces blood pressure (BP) and heart rate (HR) in the spontaneously hypertensive rat (SHR). We investigated the hypothesis that the response to nitroxides is determined by SOD mimetic activity or lipophilicity. Groups (n = 6-10) of anesthetized SHRs received graded intravenous doses of Ns: tempol (T), 4-amino-tempo (AT), 4-oxotempo (OT), 4-trimethylammonium-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT-1), 3-carbamoyl-proxyl (3-CP), or 3-carboxyproxyl (3-CTPY). Others received native or liposomal (L) Cu/Zn SOD. T and OT are uncharged, AT is positively charged and cell-permeable, and CAT-1 is positively charged and cell-impermeable. 3-CP and 3-CTPY have five-member pyrrolidine rings, whereas T, AT, OT, and CAT-1 have six-member piperidine rings. T and AT reduced mean arterial pressure (MAP) similarly (-48 [+ or -] 2 mmHg and -55 [+ or -] 8 mmHg) but more (P < 0.05) than OT and CAT-1. 3-CP and 3-CTPY were ineffective. The group mean change in MAP with piperidine Ns correlated with SOD activity (r = -0.94), whereas their E[D.sub.50] correlated with lipophilicity (r = 0.89). SOD and L-SOD did not lower BP acutely but reduced it after 90 min (-32 [+ or -] 5 and -31 [+ or -] 6 mmHg; P < 0.05 vs. vehicle). Pyrrolidine nitroxides are ineffective antihypertensive agents. The antihypertensive response to piperidine Ns is predicted by SOD mimetic action, and the sensitivity of response is by hydrophilicity. SOD exerts a delayed hypotensive action that is not enhanced by liposome encapsulation, suggesting it must diffuse to an extravascular site. tempol; superoxide dismutase; blood pressure; nitric oxide; hypertension.

Renal oxygen tension is substantially lower in the medulla than in the cortex and is reduced in hypertensive rats, a model of oxidative stress. Expression of NADPH oxidase, the primary source for superoxide anion ([O.sup.-.sub.2]*) in the kidney, is elevated in hypertension. Because molecular oxygen ([O.sub.2]) is required for [O.sup.-.sub.2]* formation, we tested the hypothesis that renal NADPH oxidase activity is limited by low [O.sub.2]. [O.sup.-.sub.2]* production by rat kidney tissue or cultured cells exposed to levels of P[O.sub.2] that mimics those in the kidney was assessed by lucigenin-enhanced chemiluminescence. NADPH-dependent [O.sup.-.sub.2]* production by kidney homogenates decreased reversibly by 60-90% after graded reductions of ambient [O.sub.2] from 10 to 0% (76 to 2 mmHg P[O.sub.2]). The NADPH-dependent [O.sup.-.sub.2]* production by the kidney homogenate was reduced by decreasing P[O.sub.2] below ~30 mmHg. The response of tissue homogenates to low P[O.sub.2] was not different between normotensive and hypertensive rats. Similarly, NADPH-dependent [O.sup.-.sub.2]* production was lower during 2% [O.sub.2] compared with 10% [O.sub.2] in rat proximal tubule cells (-57 [+ or -] 1%), vascular smooth muscle (-42 [+ or -] 5%), cardiomyocytes (-57 [+ or -] 1%), and mouse inner medulla collecting duct cells (-58 [+ or -] 3%). We conclude that [O.sup.-.sub.2]* production by NADPH oxidase is dependent on availability of [O.sub.2]. Therefore, [O.sup.-.sub.2]* generation may be limited in the kidney, both in the normal renal medulla and in the cortex of hypertensive kidneys. reactive oxygen species; hypertension; hypoxia

A thromhoxane prostanoid receptor (TP-R) agonist U-46,619 enhances tubuloglomerular feedback (TGF). Glomerular expression of TP-R and enhancement of TGF by U-46,619 increase with salt intake. We investigated the hypothesis that 8-isoprostaglandin [F.sub.2[alpha]] (8-Iso) activates TGF via TP-R. The maximal TGF response in rats was assessed from the fall in proximal stop flow pressure (PSF; an index of glomerular capillary pressure) during loop of Henle (LH) microperfusion of artificial tubular fluid (ATF) at 40 nl/min. Microperfusion of 8-Iso ([10.sup.-4] M) into the efferent arteriole (EA) enhanced TGF responses by 20 [+ or -] 3% (P < 0.01). TGF response to 8-Iso was independent of dietary salt [[DELTA]TGF%, low salt (LS): 21 [+ or -] 5%; normal salt (NS): 17 [+ or -] 4%; high salt (HS): 29 [+ or -] 8%, not significant (ns)], unlike the salt-dependent effect of U-46,619 ([DELTA]TGF%, LS: 41 [+ or -] 5%; NS: 52 [+ or -] 4%; HS: 112 [+ or -] 21%). Ifetroban, the TP-R antagonist, abolished TGF responses to 8-Iso and U-46,619 at all levels of salt intake. During luminal perfusion of N-monomethyl-L-arginine (L-NMA), the effect of 8-Iso on TGF was enhanced in NS and HS but not in LS (LS: 22 [+ or -] 6 vs. LS + L-NMA: 28 [+ or -] 6%, ns; NS: 18 [+ or -] 4 vs. NS + L-NMA: 40 [+ or -] 4, P < 0.01; HS: 27 [+ or -] 3 vs. HS + L-NMA: 65 [+ or -] 6, P < 0.01). However, U-46,619 did not further increase TGF after L-NMA in all salt groups (LS: 43 [+ or -] 7 vs. LS + L-NMA: 51 [+ or -] 6, ns; NS: 52 [+ or -] 7 vs. NS + L-NMA: 48 [+ or -] 8, ns; HS: 114 [+ or -] 21 vs. HS [+ or -] L-NMA: 74 [+ or -] 22, ns). In conclusion, activation of TP receptors by U-46,619 and 8-IsoPG[F.sub.2[alpha]] enhances TGF. In addition, the effect of U-46,619 was salt dependent, whereas the effect of 8-Iso-PG[F.sub.2[alpha]] was salt independent. However, stimulation of NO by 8-isoprostanes masks its salt-sensitive effect on TGF. 8-1soprostaglandin [F.sub.2[alpha]] oxygen radicals; oxidative stress; tubuloglomerular feedback response; thromboxane [A.sub.2]; nitric oxide synthase; ifetroban

We tested whether chronic ANG II infusion into rats affects descending vasa recta (DVR) contractility, synthesis of superoxide, or synthesis of nitric oxide (NO). Rats were infused with ANG II at 250 ng x [kg.sup.-1] x [min.sup.-1] for 11-13 days. DVR were loaded with dihydroethidium (DHE) to measure superoxide and 3-amino-4-aminomethyl-2',7'-difluorofluorescein (DAFFM) to measure NO. Acute constriction of DVR by ANG II (0.1, 1, and 10 nM) was diminished, and NO generation rate was raised by chronic ANG II infusion. DHE oxidation by DVR from ANG II-infused rats was similar to controls and was significantly higher when NO synthesis was prevented with [N.sup.[omega]]-nitro-L-arginine methyl ester (L-NAME). The superoxide dismutase mimetic Tempol (1 mM) increased NO generation compared with controls. The increased synthesis of NO by chronic ANG II-treated vessels persisted in the presence of Tempol. DVR endothelial cytoplasmic [Ca.sup.2+] response to ACh was diminished by chronic ANG II treatment, but the capacity of ACh to increase NO generation was unaltered. We conclude that DVR generation of superoxide is not affected by chronic ANG II exposure but that basal NO synthesis is increased. DVR superoxide is unlikely to be an important mediator of chronic ANG II slow pressor hypertension in rats. medulla; kidney; microcirculation; calcium; oxidative stress

We tested the hypothesis that superoxide anion ([O.sup.-.sub.2]*) generated in the kidney by prolonged angiotensin II (ANG II) reduces renal cortical P[o.sub.2] and the use of [O.sub.2] for tubular sodium transport ([T.sub.Na]:Q[O.sub.2]). Groups (n = 8-11) of rats received angiotensin II (ANG II, 200 ng x [kg.sup.-1] x [min.sup.-1] sc) or vehicle for 2 wk with concurrent infusions of a permeant nitroxide SOD mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (Tempol, 200 nmol x [kg.sup.-1] x [min.sup.-1]) or vehicle. Rats were studied under anesthesia with measurements of renal oxygen usage and P[O.sub.2] in the cortex and tubules with a glass electrode. Compared with vehicle, ANG II increased mean arterial pressure (107 [+ or -] 4 vs. 146 [+ or -] 6 mmHg; P < 0.001), renal vascular resistance (42 [+ or -] 3 vs. 65 [+ or -] 7 mmHg x [ml.sup.-1] x [min.sup.-1] x 100 [g.sup.-1] ; P < 0.001), renal cortical NADPH oxidase activity (2.3 [+ or -] 0.2 vs. 3.6 [+ or -]] 0.4 nmol [O.sup.-.sub.2]* x [min.sup.-1] x [mg.sup.-1] protein: P < 0.05), mRNA and protein expression for p[22.sup.phox] (2.1- and 1.8-fold respectively; P < 0.05) and reduced the mRNA for extracellular (EC)-SOD (-1.8 fold; P < 0.05). ANG II reduced the P[O.sub.2] in the proximal tubule (39 [+ or -] 1 vs. 34 [+ or -] 2 mmHg; P < 0.05) and throughout the cortex and reduced the [T.sub.Na]:Q[O.sub.2] (17 [+ or -] 1 vs. 9 [+ or -] 2 [micro]mol/[micro]mol; P < 0.001). Tempol blunted or prevented all these effects of ANG II. The effects of prolonged ANG II to cause hypertension, renal vasoconstriction, renal cortical hypoxia, and reduced efficiency of [O.sub.2] usage for [Na.sup.+] transport, activation of NADPH oxidase, increased expression of p[22.sup.phox], and reduced expression of EC-SOD can be ascribed to [O.sup.-.sub.2]* generation because they are prevented by an SOD mimetic. reactive oxygen species; superoxide dismutase; TEMPOL; nitroxides; NADPH oxidase; hypertension

TP receptors regulate renal hemodynamics during angiotensin II slow pressor response. Am J Physiol Renal Physiol 287: F753-F759, 2004. First published June 22, 2004; 10.1152/ajprenal.00423.2003.--We investigated the hypothesis that thromboxane [A.sub.2] (Tx[A.sub.2])-prostaglandin [H.sub.2] receptors (TP-Rs) mediate the hemodynamic responses and increase in reactive oxygen species (ROS) to ANG II (400 ng x [kg.sub.-1] x [min.sub.-1] sc for 14 days) using TP-R knockout (TP -/-) and wild-type (+/+) mice. TP -/- had normal basal mean arterial blood pressure (MAP) and glomerular filtration rate but reduced renal blood flow and increased filtration fraction (FF) and renal vascular resistance (RVR) and markers of ROS (thiobarbituric acid-reactive substances and 8-isoprostane PG[F.sub.2[alpha]]) and nitric oxide (NOx). Infusion of ANG II into TP +/+ increased ROS and thromboxane [B.sub.2] (Tx[B.sub.2]) and increased RVR and FF. ANG II infusion into TP -/- mice reduced ANG I and increased aldosterone but caused a blunted increase in MAP (TP -/-: +6 [+ or -] 2 vs. TP +/+: +15 [+ or -] 3 mmHg) and failed to increase FF, ROS, or Tx[B.sub.2] but increased NOx and paradoxically decreased RVR (-2.1 [+ or -] 1.7 vs. +2.6 [+ or -] 0.8 mmHg*[ml.sup.-1]*[min.sup.-1]*[g.sup.-1]). Blockade of A[T.sub.1] receptor of TP -/- mice infused with ANG II reduced MAP (-8 mmHg) and aldosterone but did not change the RVR or ROS. In conclusion, during an ANG II slow pressor response, A[T.sub.1] receptors activate TP-Rs that generate ROS and prostaglandins but inhibit NO. TP-Rs mediate all of the increase in RVR and FF, part of the increase in MAP, but are not implicated in the suppression of ANG I or increase in aldosterone. TP -/- mice have a basal increase in RVR and FF associated with ROS. thromboxane [A.sub.2]-prostaglandin [H.sub.2] receptor; isoprostane; hypertension; renal vascular resistance

Oxidative stress accompanies angiotensin (ANG) II infusion, but the role of ANG type 1 vs. type 2 receptors (A[T.sub.1]-R and A[T.sub.2]-R, respectively) is unknown. We infused ANG II subcutaneously in rats for 1 wk. Excretion of 8-isoprostaglandin [F.sub.2[alpha]] (8-Iso) and malonyldialdehyde (MDA) were related to renal cortical mRNA abundance for subunits of NADPH oxidase and superoxide dismutases (SODs) using real-time PCR. Subsets of ANG II-infused rats were given the A[T.sub.1]-R antagonist candesartan cilexetil (Cand) or the A[T.sub.2]-R antagonist PD-123,319 (PD). Compared to vehicle (Veh), ANG II increased 8-Iso excretion by 41% (Veh, 5.4 [+ or -] 0.8 vs. ANG II, 7.6 [+ or -] 0.5 pg/24 h; P < 0.05). This was prevented by Cand (5.6 [+ or -] 0.5 pg/24 h; P < 0.05) and increased by PD (15.8 [+ or -] 2.0 pg/24 h; P < 0.005). There were similar changes in MDA excretion. Compared to Veh, ANG II significantly (P < 0.005) increased the renal cortical mRNA expression of p[22.sup.phox] (twofold), Nox-1 (2.6-fold), and Mn-SOD (1.5-fold) and decreased expression of Nox-4 (2.1-fold) and extracellular (EC)-SOD (2.1-fold). Cand prevented all of these changes except for the increase in Mn-SOD. PD accentuated changes in p[22.sup.phox] and Nox-1 and increased p[67.sup.phox]. We conclude that ANG II infusion stimulates oxidative stress via A[T.sub.1]-R, which increases the renal cortical mRNA expression of p[22.sup.phox] and Nox-1 and reduces abundance of Nox-4 and EC-SOD. This is offset by strong protective effects of A[T.sub.2]-R, which are accompanied by decreased expression of p[22.sup.phox], Nox-1, and p[67.sup.phox]. candesartan; isoprostane; angiotensin receptor blocker; PD-123,319; malonyldialdehyde

Renal medullary cells are exposed to elevated and variable osmolarities and low oxygen tension. Despite the harsh environment, these cells are resistant to the effects of many harmful events. To test the hypothesis that this resistance is a consequence of these cells developing a stress tolerance phenotype to survive in this milieu, we created osmotically tolerant cells [hypertonic (HT) cells] by gradually adapting murine inner medullary collecting duct 3 cells to hyperosmotic medium containing NaC1 and urea. HT cells have a reduced DNA synthesis rate, with the majority of cells arrested in the [G.sub.0]/[G.sub.1] phase of the cell cycle, and show constitutive expression of heat shock protein 70 that is proportional to the degree of hyperosmolarity. Unlike acute hyperosmolarity, chronic hyperosmolarity failed to activate MAPKs. Moreover, HT cells acquired protein translational tolerance to further stress treatment, suggesting that HT ceils have an osmotolerant phenotype that is analogous to thermotolerance but is a permanent condition. In addition to osmotic shock, HT cells were more resistant to heat, [H.sub.2][O.sub.2], cyclosporin, and apoptotic inducers, compared with isotonic murine inner medullary duct 3 cells, but less resistant to amphotericin B and cadmium. HT cells demonstrate that in renal medullary cells, hyperosmotic stress activates biological processes that confer cross-tolerance to other stressful conditions. heat shock protein 70; nephrotoxins; thermotolerance; cell cycle; inner medullary collecting duct 3

A TP receptor (TP-R) mimetic causes salt-sensitive hypertension and renal afferent arteriolar vasoconstriction. TP-Rs mediate effects of ANG II on renal vascular resistance and drinking. Therefore, we investigated the hypothesis that thromboxane [A.sub.2] synthase (Tx[A.sub.2]-S) and/or TP-R expression is regulated by salt and/or ANG II. Rats (n = 6) received high-salt (HS) or low-salt (LS) diets. Additional HS-diet rats received ANG II while other HS- and LS-diet rats received the A[T.sub.1] receptor (A[T.sub.1]-R) antagonist losartan. Excretion of thromboxane [B.sub.2] by conscious rats was increased with the HS diet compared with the LS diet (126 [+ or -] 10 vs. 48 [+ or -] 5 pmol/24 h, respectively; P < 0.01). The mRNA abundance for TP-Rs (relative to [beta]-actin) in the kidney cortex was enhanced 30% by the HS diet (P < 0.001) and was reduced 50% by the addition of ANG II (P < 0.001). However, during losartan administration, the effects of salt were reversed; mRNA more than doubled during the LS diet (P < 0.001). Similarly, the mRNA abundance for TP-Rs in the brain stem was reduced by 50% with the addition of ANG II (P < 0.001) and during losartan administration was almost doubled by the LS diet (P < 0.001). The mRNA abundance for Tx[A.sub.2]-S in the kidney cortex also was increased many times with the HS diet (P < 0.001). In contrast, the mRNA for Tx[A.sub.2]-S in the brain was unaffected by salt. ANG II did not affect Tx[A.sub.2]-S at either site. During losartan administration, Tx[A.sub.2]-S increased modestly in the brain stem with the LS diet. mRNA abundance for TP-Rs in the kidney cortex and brain stem is suppressed, by ANG II acting on A[T.sub.1]-Rs. In the absence of A[T.sub.1]-Rs, expression of TP-Rs at both sites is enhanced by LS intake. In contrast, ANG II does not affect the mRNA abundance for Tx[A.sub.2]-S. Expression of Tx[A.sub.2]-S is enhanced by HS intake in the kidney cortex but by LS intake in the brain stem only during losartan administration. Thus TP-Rs are strongly dependent on ANG II acting on AT1-Rs, whereas TxA2-S is regulated differentially in the kidney cortex and brain stem by salt intake. thromboxane [A.sub.2]; prostaglandins; angiotensin II; losartan; angiotensin receptor blocker; thromboxane prostanoid receptor

In screening for drug discovery, chemists often select a large subset of molecules from a very large database (e.g., select 1,000 molecules from 100,000). To generate diverse leads for drug [...]

Central angiotensin II (ANG II) regulates thirst. Because thromboxane [A.sub.2]-prostaglandin [H.sub.2] (TP) receptors are expressed in the brain and mediate some of the effects of ANG II in the vasculature, we investigated the hypothesis that TP receptors mediate the drinking response to intracerebroventricular (icv) injections of ANG II. Pretreatment with the specific TP-receptor antagonist ifetroban (Ifet) decreased water intake with 50 ng/kg icy ANG II (ANG II + Veh, 7.2 [+ or -] 0.7 ml vs. ANG II + Ifet, 2.8 [+ or -] 0.8 ml; n = 5 rats; P < 0.001) but had no effect on water intake induced by hypertonic saline (NaCl + Veh, 8.4 [+ or -] 1.1 ml vs. NaCl + Ifet, 8.9 [+ or -] 1.8 ml; n = 5 rats; P = not significant). Administration of 0.6 [micro]g/kg icy of the TP-receptor agonist U-46,619 did not induce drinking when given alone but did increase the dipsogenic response to a near-threshold dose of 15 ng/kg icv ANG II (ANG II + Veh, 1.1 [+ or -] 0.7 vs. ANG II + U-46,619, 4.5 [+ or -] 0.9 ml; n = 5 rats; P < 0.01). We conclude that central TP receptors contribute to the dipsogenic response to ANG II. drinking; ifetroban; TP receptors; U-46,619

A problem often arising in engineering applications of computer models is to determine the importance of each data item in the large pool of required input factors. This paper explores a statistical approach for investigating factor sensitivities. The methodology is demonstrated with the HDM-III highway life-cycle cost analysis model. Specifically, the net present value (NPV) of life-cycle costs predicted by the HDM-III model is analyzed, and sensitivities of NPV to the link characterization input factors are investigated. In the statistically designed experiment, combinations of the input factors are chosen using a method called Latin hypercube sampling, which is well suited to the deterministic HDM-III model. Two analyses of the output data are performed, based on a first-order regression approximation and a Gaussian stochastic-process model. For NPV, the factor rankings are similar, but the sensitivities obtained from the two techniques show some marked differences. This demonstrates the greater flexibility of the stochastic-process model in dealing with nonlinearities and factor interactions in complex input-output relationships.

The spontaneously hypertensive rat (SHR) has an increased tubuloglomerular feedback (TGF) and a reduced buffering by juxtaglomerular apparatus (JGA)-derived NO. The hypothesis that these effects are caused by reductions in nitric oxide synthase (NOS) expression or limited availability of L-arginine or tetrahydrobiopterin (BH4). Findings showed that there is a decreased role for NO from neuronal NOS in blunting TGF in SHR which cannot be caused by limited NOS expression or availability of substrate or BH4.

The synthesis of nitric oxide by the neuronal nitric oxide synthase during salt loading in rats is investigated using enzyme inhibition studies and diuresis manipulation using furosemide. The generation of nitric oxide was monitored by measuring the excretion of metabolites. Results reveal that the increase in nitric oxide synthesis is brought about by an increase in the activity of neuronal nitric oxide synthase and solute reabsorption in the macula densa.

A study was conducted to test whether a proposed pathway of chaperone interactions is operative in the early stages of protein synthesis in animal cells. Cells at near confluence were incubated for heat shock treatments while immunoprecipitation was carrier out to analyze protein-protein relationships. Results indicated that the molecular chaperones hdj-1p and 2p did not directly interact with nascent and newly synthesized polypeptide populations in mammalian cells.

Research shows that thromboxane A2 (TxA2) and prostaglandin endoperoxide (PGH2) receptor activity is boosted by high-salt intake in rats. Experiments designed to assess tubuloglomerular feedback responses to TXA2/PGH2 mimetic using male Sprague-Dawley rats are described. TxA2 activity measurements in relation to low and high salt intake are illustrated. Renal vasoconstriction responses to receptor feedback are discussed.

A study was conducted on the role of arginine vasopressin (AVP) in pressor responses during activation of central TxA2/PGH2 receptors. The method involved the injection of an agonist into the lateral cerebral ventricle of rats. The findings suggest that TxA2/PGH2-receptor agonist U-46619 increases blood pressure and releases AVP through brain receptor activation. Moreover, AVP is responsible for one-half of the pressor response.

An investigation of the sympathetic nervous system and hypertension during prolonged thromboxane/prostaglandin H2 receptor activation was conducted to determine its effects on the sympathetic nervous system of rats. The mean arterial pressure (MAP) was measured using implanted flow probes. Results of the study indicated that hypertension during prolonged infusions of U-46619 into salt-loaded rats leads to an increase in total and renal vascular resistance.

The presence of thromboxane A2 (TxA2) and prostaglandin H2 (PGH2) receptors in rat neural and glial cells was analyzed to determine blood pressure responses to the TxA2 mimetic, U-46,619. Intracerebrovascular administration of U-46,619 enhanced the pressor responses of rats fed on a high-salt diet. However, intravenous and intracerebrovascular administration of ifetroban attenuated the effects of U-49,619 on pressor response. The effects of U-46,619 indicated the presence of TxA2/PGH2 receptor messenger RNAs in rat neurons, glial and brain stem.

The interferon-induced double-stranded RNA-activated protein kinase, PKR, likely contributes to both the antiviral and the antiproliferative effects of interferon. We previously found that influenza virus avoids the translational inhibitory effects of activated PKR by activating a cellular inhibitory protein, termed [P58.sup.IPK], based on its [M.sub.r] of 58,000. [P58.sup.IPK] is a member of the tetratricopeptide family of proteins and possesses significant homology to the conserved J region of the DnaJ family of heat shock proteins. We earlier hypothesized that [P58.sup.IPK] was kept in an inactive state with its own inhibitor (termed I-[P58.sup.IPK]) in uninfected cells. We therefore attempted the purification and characterization of I-[P58.sup.IPK]. The following data suggest that we have identified the molecular chaperone, hsp40, as I-[P58.sup.IPK]. (i) The MonoP-purified I-[P58.sup.IPK] protein reacted with hsp40 antibody. (ii) This preparation demonstrated high specific activity in an in vitro functional assay containing only purified recombinant and native components. (iii) Purified, recombinant hsp40 protein inhibited [P58.sup.IPK] in an identical in vitro assay. (iv) Finally, we demonstrate that hsp40 directly complexes with [P58.sup.IPK], in vitro, suggesting the inhibition occurs through a direct interaction. Our data, taken together, provide evidence for a novel intersection between the heat shock and interferon pathways, and suggest that influenza virus regulates PKR activity through the recruitment of a cellular stress pathway.

The hypertensive action of angiotensin II type I (AT1) and thromboxane A2/prostaglandin endoperoxide (TxA2/PGH2) receptor antagonists was analyzed in two-kidney,one-clip (2k,1C) Goldblatt rat models of hypertension. A marked reduction in blood pressure during the early, intermediate and late phase of renovascular hypertension was detected in 2K,1C Goldblatt rats after the three-day administration of AT1 or TxA2/PGH2 receptors antagonist. However, hypertension from the early to the late phase was reversed by lorsartan and ifetroban.

Analysis of neuroblastoma scrapie-infected N2a (ScN2a) cells for the expression and cellular distribution of heat shock proteins (Hsp) to find whether proteins participate in the transformation of cellular prion protein into the scrapie isoform PrP(super Sc) shows changes in subcellular translocations of particular Hsps in ScN2a cells. This may represent cellular response to the collection of PrP(super Sc). The distribution of Hsp73 was unaffected by heat shock.

Renal blood flow (RBF) rates measured using miniature ultrasonic transit-time flow probes that are calibrated using excised arteries at different hematocrit (Hct) and flow rates exhibit a high correlation with true flow rates at subnormal and normal Hct values. In vivo RBF measurements with the excretion and extraction of P-aminohippuric acid correlate well over a broad range of flow rates, indicating that the use of ultrasonic transit-time flow meter enables accurate measurement of RBF in anesthetized, instrumented rats.

70-kD heat-shock proteins (hsp70) are involved in the peroxisomal import of proteins in mammals. The hsp70 molecules are situated on the outer surface of the peroxisomal membrane and their concentration increases with the peroxisomal growth. Antibodies developed against hsp70 proteins inhibit the protein import that is overcome by exogenous hsp70 protein treatment.

The high molecular weight intermediate of the homomultimeric hepatitis B virus capsid is related to an eukaryotic cytosolic chaperonin. The isolated high molecular weight intermediate produces mature capsids. The chaperonin t-complex polypeptide 1 (TCP-1)-associated 60-KD protein is related to polypeptides from two different intermediate units. The mature capsids differ from viral capsids, indicating the function of the eukaryotic cytosolic chaperonin in monomer folding.

Heat shock protein (hsp) 73 and hsp 72 represent inducible and constitutive forms of heat shock proteins, respectively. Immunoprecipitation and gel electrophoretic analyses showed that hsp 73 and 72 interact with one another. Double-label immunofluorescence and microinjection experiments confirmed this interaction in vivo. Furthermore, the interaction between these two heat shock proteins required the presence of ATP. The implications of this ATP-dependent interaction is discussed in regard to the structure and function of these proteins in normal and stressed cells.

The hypothesis stating that arginine-derived nitric oxide (NO) mediates a vasodilator arm of the tubuloglomerular feedback response was tested. Immunohistochemical analysis revelaed the presence of NO synthase in the macula densa of the kidney, localizing it to the tubular epithelial cells adjacent to the afferent arteriole of cortical nephrons. Based on the effects of various drugs, it was shown that the NO formed in the macula densa mediates vasorelaxation of the afferent arteriole. These results demonstrate that NO synthase, its target enzyme guanylyl cyclase and cGMP are new vasodilator components of the tubuloglomerular feedback response.

Transcription regulation of gene expression of heat shock proteins was found to be correlative to protein synthesis regulation and denatured protein accumulation subjected to stress. Stress denaturation of proteins activated hsp gene transcriptional expression, but decrease in the number of nascent polypeptides suppressed the transcription activation. These observations implied the ability of cells to combine modifications in denatured and still-unfolded nascent polypeptides. An hsp similar to hsp70 is believed to be the linking factor involved in the regulatory processes.

The effects of metabolic stress on the folding pathway of developing proteins and their responses to induced stress were investigated. Cells exposed to amino acid analog or sodium arsenite exhibited inability of newly synthesized proteins to properly fold and remained attached to their respective heat-shock protein (hsp) 70. Maturing proteins became insolouble upon heat shock treatment and showed increased number of hsp 72/73. ATP depletion in cells resulted in the inhibition of hsp 70 release from developing proteins. The results indicated that the effects and responses of proteins to metabolicstress depend on the kind and severity of the induced stress.

The effect of heat insult on human progesterone receptors isolated from T47D breast cancer cells associated with two heat shock proteins (hsp) was examined. Results show that heat treatment reduced receptor-hsp interaction. However, receptors still complexed with hsp retained its hormone- and DNA-binding properties. Heat treatment also stimulated receptor activity attributed to the generation of more hsp. Chemical insult producing greater hsp production response also had a greater stimulatory effect on the receptor. This indicate that the intensity of hsp and receptor responses is dependent on the severity of the insult.

All human [gamma delta] T cells coexpressing the products of the variable (V) region T cell receptor (TCR) gene segments [V.sub.gamma]9 and [V.sub.delta]2 recognize from some mycobacterial extracts and Daudi [...]

A general method for constructing permutation tests for various experimental designs follows from invariance and sufficiency. In this framework, randomization (or rerandomization) tests arc just special cases of permutation tests. The methodology extends the applicability of permutation tests: An example demonstrates a test for an interaction effect in a factorial experiment, a problem thought to be unapproachable by permutation or randomization methods. Tests are constructed as follows. The modeling of block and treatment effects closely parallels classical analysis of variance (ANOVA). The ANOVA assumptions of iid normal random errors are replaced, however, by the much weaker assumption of exchangeability of subsets of random errors. Distributional dependences on the unknown nuisance parameters for blocks, covariates, and untested treatments and on the unknown error distribution are eliminated by invariance and sufficiency, respectively. Initial reduction of the data by invariance appears to extend considerably the applicability of permutation tests. Because of the assumed exchangeability of the errors, the sufficiency step leads to data permutations when computing the test. The method also addresses some philosophical problems associated with randomization tests. For instance, in this article's framework, it is the design, and not the data, which is always regarded as fixed, so ancillarity of the design causes no difficulty. KEY WORDS: Exchangeability; Randomization; Randomization test; Rerandomization test., 1. INTRODUCTION Pitman (1937a, b, c) developed permutation tests for two-sample problems, simple linear regression, and block-designs. Only exchangeability of errors within certain subsets is assumed, yet these tests can [...]

Interaction of Hsp 70 with Newly Synthesized Proteins: Implications for Protein Folding and Assembly IN MOST ORGANISMS ADVERSE changes in the local environment result in increased expression of heat shock [...]

Hsp60 and Hsp70, the molecular chaperone proteins, bind themselves to short peptides and unfolded proteins when twisted in the cell functions under stress induced and normal conditions. The disintegration of the substrate polypeptides from the chaperone is caused by the addition of Mg-ATP, and occurs since the ATP analogue is not capable of replacing ATP. The disintegration Hsp 70-substrate proteins require the hydrolysis of the Mg-ATP in addition to the earlier mentioned reactions. Mg-ATP binding is more essential than the Mg-ATP hydrolysis to the disintegration of the molecular chaperone proteins.

Kitiyakara, Chagriya, Tina Chabrashvili, Pedro Jose, William J. Welch, and Christopher S. Wilcox. Effects of dietary salt intake on plasma arginine. Am J Physiol Regulatory Integrative Comp Physiol 280: R1069-R1075, 2001.--Because L-arginine is degraded by hepatic arginase to ornithine and urea and is transported by the regulated 2A cationic amino acid [y.sup.+] transporter (CAT2A), hepatic transport may regulate plasma arginine concentration. Groups of rats (n = 6) were fed a diet of either low salt (LS) or high salt (HS) for 7 days to test the hypothesis that dietary salt intake regulates plasma arginine concentration and renal nitric oxide (NO) generation by measuring plasma arginine and ornithine concentrations, renal NO excretion, and expression of hepatic CAT2A, and arginase. LS rats had lower excretion of NO metabolites and cGMP, lower plasma arginine concentration (LS: 83 [+ or -] 7 vs. HS: 165 [+ or -] 10 [micro]mol/l, P [is less than] 0.001), but higher plasma ornithine concentration (LS: 82 [+ or -] 6 vs. HS: 66 [+ or -] 4 [micro]mol/l, P [is less than] 0.05) and urea excretion. However, neither the in vitro hepatic arginase activity nor the mRNA for hepatic arginase I was different between groups. In contrast, LS rats had twice the abundance of mRNA for hepatic CAT2A (LS: 3.4 [+ or -] 0.4 vs. HS: 1.6 [+ or -] 0.5, P [is less than] 0.05). The reduced plasma arginine concentration with increased plasma ornithine concentration and urea excretion during LS indicates increased arginine metabolism by arginase. This cannot be ascribed to changes in hepatic arginase expression but may be a consequence of increased hepatic arginine uptake via CAT2A. nitric oxide; system [y.sup.+] transport; cationic amino acid transporter; ornithine; urea