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Angiotensin II plays an important role in vascular remodeling through effects that involve, in part, interactions of vascular smooth muscle cells with extracellular matrix via integrins, which belong to a family of transmembrane receptors. We hypothesized that angiotensin (Ang) II regulates expression of vascular integrins and their ligands in experimental hypertension. Rats were infused subcutaneously with Ang II and received angiotensin type-1 (AT1) receptor blocker losartan, the AT1/angiotensin type-2 (AT2) [Sar1-Ile8]-Ang II, or the vasodilator hydralazine for 7 days. Osteopontin and integrin subunit expression were evaluated immunohistochemically. Ang II enhanced vascular alpha8, beta1, beta3 integrins and osteopontin expression, which were significantly reduced by losartan, [Sar1-Ile8]-Ang II, and hydralazine. Although Ang II increased vascular alpha5 subunit expression, this was additionally increased by losartan. Losartan was the only treatment that induced alpha1 subunit expression. These results demonstrate that AT1 and AT2 receptors have countervailing effects on vascular integrin subunit expression that may influence their effects on vascular remodeling and extracellular matrix composition.

We investigated the role of angiotensin II type 1 (AT1) and AT2 receptors, matrix metalloproteinases (MMPs), and extracellular matrix (ECM) components involved in vascular remodeling of resistance arteries induced by angiotensin II (Ang II). Sprague-Dawley rats received Ang II (120 ng/kg per minute SC) +/- the AT1 antagonist losartan (10 mg/kg per day PO), the AT1/AT2 antagonist Sar1-Ile8-Ang II (Sar-Ile; 10 microg/kg per minute SC), or hydralazine (25 mg/kg per day PO) for 7 days. Structure and mechanical properties of small mesenteric arteries were evaluated on a pressurized myograph. Ang II increased growth index (+21%), which was partially decreased by losartan (-11%) and abrogated by Sar-Ile. Hydralazine markedly increased growth index (+32%) despite systolic blood pressure (BP) lowering, suggesting a BP-independent effect of Ang II on vascular growth. Elastic modulus was increased by Sar-Ile compared with Ang II and control. Vascular type I collagen was reduced (P<0.05), whereas fibronectin increased significantly with Sar-Ile. Vascular tissue inhibitor of metalloproteinase-2 binding to MMP-2 was abrogated by Sar-Ile, but MMP-2 activity was significantly increased compared with losartan, Ang II, and controls. Thus, AT1 blockade exerted antigrowth effects and reduced stiffness of small resistance arteries by decreasing nonelastic fibrillar components (collagen and fibronectin). Concomitant AT1/AT2 blockade prevented growth, reduced collagen type I and elastin deposition but increased vascular stiffness, fibronectin, and MMP-2 activity. These results demonstrate opposing roles of AT1 receptors that increase fibronectin and vascular stiffness and AT2 receptors that decrease MMP-2 and increase elastin. Changes in vascular wall mechanics, ECM deposition, and MMP activity are thus modulated differentially by Ang II receptors.

Angiotensin IV (Ang IV) is a metabolite of the potent vasoconstrictor angiotensin II (Ang II). Because specific binding sites for this peptide have been reported in numerous tissues including the brain, it has been suggested that a specific Ang IV receptor (AT4) might exist. Bolus injection of Ang IV in brain ventricles has been implicated in learning, memory, and localized vasodilatation. However, the functions of Ang IV in a physiological context are still unknown. In this study, we generated a transgenic (TG) mouse model that chronically releases Ang IV peptide specifically in the brain. TG mice were found to be hypertensive by the tail-cuff method as compared with control littermates. Treatment with the angiotensin-converting enzyme inhibitor captopril had no effect on blood pressure, but surprisingly treatment with the Ang II AT1 receptor antagonist candesartan normalized the blood pressure despite the fact that the levels of Ang IV in the brains of TG mice were only 4-fold elevated over the normal endogenous level of Ang peptides. Calcium mobilization assays performed on cultured CHO cells chronically transfected with the AT1 receptor confirm that low-dose Ang IV can mobilize calcium via the AT1 receptor only in the presence of Ang II, consistent with an allosteric mechanism. These results suggest that chronic elevation of Ang IV in the brain can induce hypertension that can be treated with angiotensin II AT1 receptor antagonists.

In this study, we examined the role of angiotensin type 1 (AT1) receptors in the rostral ventrolateral medulla (RVLM) in mediating the pressor action of emotional stress in conscious rabbits. Rabbits were chronically instrumented with guide cannulas for bilateral microinjections into the RVLM and an electrode for measuring renal sympathetic nerve activity (RSNA). Airjet stress evoked increases in arterial pressure, heart rate, and RSNA, which reached a maximum (+9+/-1 mm Hg, +20+/-5 beats/min, and +93+/-17%, respectively) in the first 2 minutes of stress exposure. Then RSNA rapidly returned to prestress values, while arterial pressure and heart rate remained close to the maximal level until the conclusion of the 7-minute airjet exposure. Microinjections of the nonselective angiotensin receptor antagonist sarile (0.5 nmol, n=8) or AT1 receptor antagonists losartan (2 nmol, n=6) or candesartan (0.2 nmol, n=6) into the RVLM did not alter resting cardiovascular parameters. By contrast, the antagonists attenuated the sustained phase (4 to 7 minutes) of the pressor stress response by 55% to 89%. However, only sarile decreased the onset of this response. The antagonists affected neither the stress-induced tachycardia nor the pressor response to glutamate microinjections. Microinfusion of angiotensin II (4 pmol/min, n=8) into the RVLM did not change the pressor response to airjet stress but attenuated tachycardic response by 47%. Microinjections of vehicle did not alter the cardiovascular stress response. Sarile, losartan, and angiotensin II did not affect the sympathoexcitatory response to baroreceptor unloading. These results suggest that AT1 receptors in the RVLM are important in mediating the pressor effects of emotional stress in conscious rabbits.

Background: Endogenous intratubular angiotensin II (Ang II) supports an autocrine tonic stimulation of NaCl absorption in the proximal tubule, and its production may be regulated independently of circulating Ang II. In addition, endogenous Ang II activity may be regulated at the brush border membrane (BBM), by the rate of aminopeptidase A and N (APA and APN) activities and the rate of Ca2+-independent phospholipase A2 (PLA2-dependent endocytosis and recycling of the complex Ang II subtype 1 (AT1) receptor (AT1-R). The aim of the present study was to look for subcellular localization of AT1-R, and APA and APN activities in the medullary thick ascending limb of Henle (mTAL), as well as search for an asymmetric coupling of AT1-R to signal transduction pathways., Methods: Preparations of isolated basolateral membrane (BLMV) and luminal (LMV) membrane vesicles from rat mTAL were used to localize first, AT1-R by 125I-[Sar1, Ile8] Ang II binding studies and immunoblot experiments with a specific AT1-R antibody, and second, APA and APN activities. Microfluorometric monitoring of cytosolic Ca2+ with a Fura-2 probe was performed in mTAL microperfused in vitro, after apical or basolateral application of Ang II., Results: AT1-R were present in both LMV and BLMV, with a similar Kd (nmol/L range) and Bmax. Accordingly, BLMV and LMV preparations similarly stained specific AT1-R antibody. APA and APN activities were selectively localized in LMV, although to a lesser extent than those measured in BBM. In the in vitro microperfused mTAL, basolateral but not apical Ang II induced a transient increase in cytosolic [Ca2+]., Conclusions: Besides the presence of basolateral AT1-R in mTAL coupled to the classical Ca2+-dependent transduction pathways, AT1-R are present in LMV, not coupled with Ca2+ signaling, and co-localized with APA and APN activities. Thus, apical APA and APN may play an important role in modulating endogenous Ang II activity on NaCl reabsorption in mTAL.

TGR(ASrAOGEN)680, a newly developed transgenic rat line with specific downregulation of astroglial synthesis of angiotensinogen, exhibits decreased brain angiotensinogen content associated with a mild diabetes insipidus and lower blood pressure. Autoradiographic experiments were performed on TGR(ASrAOGEN) (TG) and Sprague-Dawley (SD) control rats to quantify AT(1) and AT(2) receptor-binding sites in different brain nuclei and circumventricular organs. Dose-response curves for drinking response to intracerebroventricular injections of ANG II were compared between SD and TG rats. In most of the regions inside the blood-brain barrier [paraventricular nucleus (PVN), piriform cortex, lateral olfactory tract (LOT), and lateral preoptic area (LPO)], AT(1) receptor binding (sensitive to CV-11974) was significantly higher in TG compared with SD. In contrast, in the circumventricular organs investigated [subfornical organ (SFO) and area postrema], AT(1) receptor binding was significantly lower in TG. AT(2) receptors (binding sensitive to PD-123319) were detected at similar levels in the inferior olive (IO) of both strains. Angiotensin-binding sites sensitive to both CV-11974 and PD-123319 were detected in the LPO of SD rats and specifically upregulated in LOT, IO, and most notably PVN and SFO of TG. The dose-response curve for water intake after intracerebroventricular injections showed a higher sensitivity to ANG II of TG (EC(50) = 3.1 ng) compared with SD (EC(50) = 11.2 ng), strongly suggesting that the upregulation of AT(1) receptors inside the blood-brain barrier of TG rats is functional. Finally, we showed that downregulation of angiotensinogen synthesized by astroglial cells differentially regulates angiotensin receptor subtypes inside the brain and in circumventricular organs.

Atherogenesis involves an early endothelial dysfunction hallmarked by elevated free radical production and increased adhesiveness for monocytes. It was hypothesized that activation of the tissue renin angiotensin system may contribute to the endothelial alteration. To test this hypothesis, thoracic aortae were isolated from normocholesterolemic (NC; n = 6) and hypercholesterolemic (HC; n = 6; diet: 0.5% cholesterol; 6 weeks) New Zealand white rabbits, and incubated for 2 h with the angiotensin II (Ang II) receptor antagonist Sar-1,Ile-8-Ang II, the antioxidant pyrolidine dithiocarbamate (PDTC) and the protein kinase C (PKC) antagonist staurosporin. Superoxide production from aortic segments was measured by lucigenin-enhanced chemiluminescence. In comparison to the normocholesterolemic state, hypercholesterolemia led to a significant increase in superoxide production (221 +/- 44%, p < 0.02); this was reduced by ex vivo treatment of the vessel segment with Ang II-antagonist (to 130 +/- 29%; p < 0.04 vs HC), or PKC-antagonist (to 86 +/- 26%; p < 0.001 vs HC), or PDTC (to 103 +/- 27%; p < 0.02 vs HC). Monocyte-endothelial interaction was assessed by functional binding assay. When compared to normocholesterolemic rabbits, hypercholesterolemia led to a twofold increase in monocyte binding (74 +/- 13 vs 37 +/- 4 monocytoid cells per high power field (m/hpf); p < 0.03). The Ang II-antagonist and the PKC-antagonist led to a normalization of monocyte-endothelial binding (Ang II-antagonist: 37 +/- 9 m/hpf; PKC-antagonist: 41 +/- 17 m/hpf; p < 0.05). In conclusion, these results indicate that hypercholesterolemia activates the tissue renin angiotensin system, which results in an increased endothelial production of superoxide and monocyte adhesiveness. Ang II-antagonist inhibits free radical production and monocyte adhesion through a mechanism which may include PKC.

The peptidic ANG II receptor antagonists [Sar(1),Ile(8)]ANG II (sarile) or [Sar(1),Thr(8)]ANG II (sarthran) are known to decrease arterial pressure and sympathetic activity when injected into the rostral part of the ventrolateral medulla (VLM). In anesthetized rabbits and rats, the profound depressor and sympathoinhibitory response after bilateral microinjections of sarile or sarthran into the rostral VLM was unchanged after prior selective blockade of angiotensin type 1 (AT(1)) and ANG-(1---7) receptors, although this abolished the effects of exogenous ANG II. Unlike the neuroinhibitory compounds muscimol or lignocaine, microinjections of sarile in the rostral VLM did not affect respiratory activity. Sarile or sarthran in the caudal VLM resulted in a large pressor and sympathoexcitatory response, which was also unaffected by prior blockade of AT(1) and ANG-(1---7) receptors. The results indicate that the peptidic ANG receptor antagonists profoundly inhibit the tonic activity of cardiovascular but not respiratory neurons in the VLM and that these effects are independent of ANG II or ANG-(1---7) receptors.

1. We visualized the changes in intracellular Ca2+ concentration ([Ca2+]i), using fluo-3 as an indicator, in individual smooth muscle cells within intact rat tail artery preparations. 2. On average in about 45 % of the vascular smooth muscle cells we found spontaneous Ca2+ waves and oscillations ( approximately 0.13 Hz), which we refer to here as Ca2+ ripples because the peak amplitude of [Ca2+]i was about one-seventh of that of Ca2+ oscillations evoked by noradrenaline. 3. We also found another pattern of spontaneous Ca2+ transients often in groups of two to three cells. They were rarely observed and are referred to as Ca2+ flashes because their peak amplitude was nearly twice as large as that in noradrenaline-evoked responses. 4. Sympathetic nerve activity was not considered responsible for the Ca2+ ripples, and they were abolished by inhibitors of either the Ca2+ pump in the sarcoplasmic reticulum (cyclopiazonic acid) or phospholipase C (U-73122). 5. Both angiotensin antagonists ([Sar1,Ile8]-angiotensin II and losartan) and an angiotensin converting enzyme inhibitor (captopril) inhibited the Ca2+ ripples. 6. The extracellular Ca2+-dependent tension borne by unstimulated arterial rings was reduced by the angiotensin antagonist by approximately 50 %. 7. These results indicate that the Ca2+ ripples are generated via inositol 1,4, 5-trisphosphate-induced Ca2+ release from the intracellular Ca2+ stores in response to locally produced angiotensin II, which contributes to the maintenance of vascular tone.

Background: We assessed the role of extracellular signal-regulated kinases (ERKs) in Ang II-stimulated contraction and associated signaling pathways in vascular smooth muscle cells (VSMCs) from human small arteries., Methods and Results: VSMCs derived from resistance arteries (<300 microm in diameter) from subcutaneous gluteal biopsies of healthy subjects (n=8) were used to assess Ang II-stimulated [Ca2+]i, pHi, and contractile responses. [Ca2+]i and pHi were measured with fura 2-AM and BCECF-AM, respectively, and contraction was measured photomicroscopically in cells grown on Matrigel matrix. To determine whether tyrosine kinases and ERKs influence Ang II-stimulated responses, cells were pretreated with 10(-5) mol/L tyrphostin A-23 (tyrosine kinase inhibitor) and PD98059 (MEK inhibitor). Ang II-stimulated MEK activity was determined by tyrosine phosphorylation of ERKs. The angiotensin receptor subtypes (AT1 and AT2) were assessed with [Sar1,Ile8]Ang II (a nonselective subtype antagonist), losartan (a selective AT1 antagonist), and PD123319 (a selective AT2 antagonist). Ang II dose-dependently increased [Ca2+]i (pD2=8.4+/-0.36, Emax=541+/-55 nmol/L), pHi (pD2=9. 4+/-0.29, Emax=7.19+/-0.01), and contraction (pD2=9.2+/-0.21, Emax=36+/-2.2%). Ang II induced rapid tyrosine phosphorylation of ERKs, which was inhibited by PD98059. Tyrphostin A-23 and PD98059 attenuated (P<0.05) Ang II-stimulated second messengers, and PD98059 reduced Ang II-induced contraction by >50%. [Sar1,Ile8]Ang II and losartan, but not PD123319, blocked Ang II-stimulated responses., Conclusions: These data demonstrate that in VSMCs from human peripheral resistance arteries, functional Ang II receptors of the AT1 subtype are coupled to signaling cascades involving Ca2+ and pHi pathways that are partially dependent on tyrosine kinases and ERKs. ERKs, the signaling cascades characteristically associated with cell growth, may play an important role in Ang II-stimulated contraction of human VSMCs.

MAP kinase stimulation is a key signaling event in the AT1 receptor (AT1R)-mediated chronic stimulation of tyrosine hydroxylase and norepinephrine transporter in brain neurons by angiotensin II (Ang II). In this study, we investigated the involvement of MAP kinase in AT1R phosphorylation to further our understanding of these persistent neuromodulatory actions of Ang II. Ang II caused a time-dependent phosphorylation of neuronal AT1R. This phosphorylation was associated with internalization and translocation of AT1R into the nucleus. MAP kinase also stimulated phosphorylation of neuronal AT1R. The conclusion that MAP kinase participates in neuronal AT1R phosphorylation and its targeting into the nucleus is supported further by the following. (1) MAP kinase-mediated phosphorylation of AT1R was blocked by the AT1R antagonist losartan; (2) AT1R co-immunoprecipitated with MAP kinase; (3) MAP kinase-kinase inhibitor PD98059 attenuated Ang II-induced phosphorylation of AT1R; and (4) PD98059 blocked Ang II-induced nuclear translocation of AT1Rs. In summary, these observations demonstrate that Ang II-induced phosphorylation of AT1R is mediated by its activation of MAP kinase. A possible role of AT1R translocation into the nucleus on persistent neuromodulatory actions of Ang II has been discussed.

Specific high-affinity (Kd = 3.4 nM) binding sites for 125I-labelled angiotensin I ([125I]Ang I) were identified on an epithelial cell line (IEC-18) derived from the rat small intestine. The sites, which also have high affinity for Ang II, are insensitive to both AT1- and AT2-specific angiotensin receptor antagonists. The rank order of potency with which various angiotensin peptides inhibited [125I]Ang I binding to the cells (Ang I > or = Ang II > Ang(1-7) > [Sar1,Ile8]-Ang II > Ang(3-8) > Ang III) also distinguishes these sites from AT1 and AT2 angiotensin receptors.

1. This study was undertaken in cultured vascular smooth muscle cells to characterize the angiotensin II (AII) AT1 receptor subtype involved in DNA synthesis because (i) the AII receptor involved in vascular proliferation has previously been characterized in vitro in rat aortic cells and identified as an AT1 subtype and (ii) molecular cloning and biochemical studies have provided evidence for the existence of different AT1 receptor subtypes. 2. In cultured rat aortic vascular smooth muscle (VSMC), exposure to AII (0.1 to 100 nM) resulted in a concentration-dependent increase in [3H]-thymidine incorporation with an EC50 of 1.41 +/- 0.51 nM. Maximal stimulation was observed in the presence of 100 nM AII and corresponded to 271 +/- 40% of basal [3H]-thymidine incorporation. 3. To characterize the AII AT1 receptor subtype involved in this effect, cells were exposed to AII (3 nM) in the absence or presence of increasing concentrations of various AII receptor antagonists. The stimulatory effect of AII (3 nM) on [3H]-thymidine incorporation in VSMC was antagonized by the non-selective AT1/AT2 receptor antagonist, [Sar1, Ile8]-AII (IC50 = 5.6 nM), by the AT1A/AT1B receptor antagonist, losartan (IC50 = 10.5 nM) and the AT1 receptor antagonist, L-158809 (IC50 = 0.20 nM). The selective AT2 receptor ligand, CGP 42112A, antagonized AII-induced [3H]-thymidine incorporation with an IC50 of 6.3 +/- 1.3 microM while the AT2/AT1B receptor antagonist, PD 123319, was found to be almost inactive (IC50 > 10 microM). 4. Under the same experimental conditions, angiotensin III (AIII) was found to be at least 50 times less potent than All with an apparent EC50 of 81.6 +/- 7.7 nM. At the highest concentration tested (10 microM),the effect of AIII corresponded to 327 +/- 61% of basal [3H]-thymidine incorporation.5. These results confirm that All can stimulate DNA synthesis in VSMC through an AT, receptor.Furthermore, the pharmacological characterization of this AT1 receptor is compatible with the ATlA receptor subtype recently described on cultured mesangial cells since (i) the ATIA/ATIB receptor antagonist losartan is active at nanomolar concentrations, (ii) micromolar concentrations of the AT2/AT1B receptor antagonist PD 123319 are ineffective at antagonizing the AII-induced [3H]-thymidine incorporation and (iii) All is at least 50 times more potent than AIII in stimulating DNA synthesis.

1. The effects of the angiotensin antagonists GR117289, losartan and Sar1Ala8-angiotensin II on the ex vivo binding of [125I]-Sar1Ile8-angiotensin II to rat liver and cortex/hippocampus (Cx/H) membranes have been investigated. 2. GR117289 (0.1-30 mg kg-1, s.c., 2 h pretreatment) caused a dose-dependent reduction in [125I]-Sar1Ile8-angiotensin II binding to both liver and cortex/hippocampus membranes. 3. Administration of a submaximal dose of GR117289 (1 mg kg-1, s.c.) indicated that the peak inhibition of binding in the liver occurred within 0.5 h, whereas the peak inhibition of binding in the Cx/H occurred 2 h after drug treatment. 4. The effect of GR117289 was long lasting. Binding was still reduced in the Cx/H 48 h after drug treatment (10 mg kg-1, s.c.) but had returned to normal 72 h after drug treatment. In the liver binding was still reduced 72 h after treatment with the same dose. 5. Losartan (1-30 mg kg-1, s.c.) was equipotent with GR117289 in its ability to reduce liver binding, but was less effective at inhibiting binding to central receptors. 6. The non-peptide antagonist Sar1Ala8-angiotensin II (3 and 10 mg kg-1) reduced binding in the liver but not in the Cx/H membranes. 7. These results suggest that, unlike the peptide antagonist Sar1Ala8-angiotensin II, the non-peptide angiotensin antagonists, GR117289 and losartan, are able to cross the blood brain barrier and occupy central angiotensin II receptors.

The adrenal glomerulosa cell is a major site of action of angiotensin II (AII), which binds to AT1 receptors to stimulate phosphoinositide hydrolysis and Ca2+ mobilization, and the subsequent production of aldosterone. All also influences adrenal growth and proliferation and promotes thymidine incorporation in adrenocortical cells. In primary cultures of bovine glomerulosa cells, AII was found to induce the expression of several early growth response genes (c-fos, c-jun, JunB, and Krox 24). This effect of AII was dose-dependent and was blocked by [Sar1,IIe8] AII and the nonpeptide antagonist DuP 753, indicating that it is mediated by the AT1 subtype of the AII receptor. ACTH, which elevates cAMP in glomerulosa cells, was a relatively weak inducer of c-fos expression but was as potent as AII in stimulating the expression of JunB. ACTH did not further enhance the maximal effect of AII on c-fos expression. The role of the AII-induced cytoplasmic Ca2+ increase in generating the c-fos response was suggested by the ability of the Ca2+ ionophore ionomycin to induce c-fos expression. However, mobilization of intracellular Ca2+ by the Ca2+ ATPase inhibitor thapsigargin, as well as the stimulation of Ca2+ influx by depolarization with potassium, were less potent stimuli of c-fos expression. Omission of Ca2+ from the extracellular medium, which abolishes the plateau phase of the AII-induced Ca2+ signal without affecting the early increase due to Ca2+ mobilization, enhanced the early phase of the AII-induced c-fos response, indicating that Ca2+ also has an inhibitory effect on the early gene response. Activation of protein kinase C by phorbol 12-myristate, 13-acetate (PMA) also stimulated c-fos expression, but the combination of PMA and ionomycin did not further increase the c-fos response. Inhibition of protein kinase C by staurosporine, or its depletion by prolonged exposure to PMA, prevented the c-fos response to PMA but only partially inhibited the response to AII, suggesting the involvement of other factors in stimulus-transcription coupling from the AT1 receptor.

Increases in renal venous pressure have been shown to consistently increase renal interstitial pressure; however, not until renal interstitial pressure is increased threefold is a natriuresis noted in normal animals. Since the intrarenal angiotensin II (Ang II) concentration has been postulated to increase with increasing renal venous pressure, the antinatriuretic action of Ang II could override the natriuretic effect of increased renal interstitial pressure. Therefore, the role of Ang II in the natriuretic response to increased renal venous pressure was examined in 10 pentobarbital-anesthetized dogs. Mean arterial pressure, renal blood flow, renal interstitial pressure, glomerular filtration rate, urinary sodium excretion, plasma renin activity, and prostaglandin E2 excretion were measured at renal venous pressures of 3, 15, and 30 mm Hg. The measurements were repeated after the administration of captopril (1 mg/kg i.v. bolus, n = 5) or [Sar1,Ile8]Ang II (50 micrograms/kg i.v. bolus + 50 micrograms/kg/hr infusion, n = 5). Under control conditions, mean arterial pressure, renal blood flow, plasma renin activity, and prostaglandin E2 excretion remained unchanged when renal venous pressure was increased. The elevations in renal venous pressure increased renal interstitial pressure from 7 +/- 2 to 12 +/- 2 and 22 +/- 4 mm Hg, while sodium excretion remained unchanged until renal venous pressure was 30 mm Hg. In the captopril-treated group, increasing renal venous pressure increased renal interstitial pressure as under control conditions; however, sodium excretion (23 +/- 4, 19 +/- 4, and 27 +/- 6 mueq/min) was not significantly increased even at the highest renal venous pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid endothelial cell migration and inhibition of thrombosis are critical for the resolution of denudation injuries to the vessel wall. Inhibition of the endothelial cell autocrine angiotensin system, with either the angiotensin-converting enzyme inhibitor lisinopril or the angiotensin II receptor antagonist sar1, ile8-angiotensin II, leads to increased endothelial cell migration and urokinase-like plasminogen activator (u-PA) activity (Bell, L., and J. A. Madri. 1990. Am. J. Pathol. 137:7-12). Inhibition of the autocrine angiotensin system with the converting-enzyme inhibitor or the receptor antagonist also leads to increased expression of the proto-oncogene c-src: pp60c-src mRNA increased 7-11-fold, c-src protein 3-fold, and c-src kinase activity 2-3-fold. Endothelial cell expression of c-src was constitutively elevated after stable infection with a retroviral vector containing the c-src coding sequence. Constitutively increased c-src kinase activity reconstituted the increases in migration and u-PA observed with angiotensin system interruption. Antisera to bovine u-PA blocked the increase in migration associated with increased c-src expression. These data suggest that increases in endothelial cell migration and plasminogen activator after angiotensin system inhibition are at least partially pp60c-src mediated. Elevated c-src expression with angiotensin system inhibition may act to enhance intimal wound closure and to reduce luminal thrombogenicity in vivo.

The in vivo access of the nonpeptide angiotensin II (Ang II) antagonist, DuP 753 (10 mg kg-1, i.v.), to Ang II receptors of rat brain was investigated by in vitro autoradiography with [125I]-[Sar1, Ile8] Ang II as a ligand. DuP 753 markedly inhibited the binding to sites which contain exclusively AT1 receptors both outside and within the blood brain barrier, such as the circumventricular organs, paraventricular hypothalamic nucleus, median preoptic nucleus and nucleus of the solitary tract. However, binding to other nuclei containing AT2 receptors was not significantly inhibited. These results demonstrate that DuP 753 and/or its active metabolite readily cross the blood brain barrier in vivo and selectively inhibit binding to AT1 receptors in specific brain nuclei.

We have identified two distinct cellular responses that occur in human astrocytes in the presence of angiotensin (Ang) peptides and are linked to specific receptor subtypes. Ang II and the N-terminal heptapeptide Ang-(1-7) stimulated release of prostaglandin (PG) E2 and PGI2 (measured as the stable metabolite 6-keto-PGF1 alpha). In contrast, only Ang II but not Ang-(1-7) activated phosphoinositide-specific phospholipase C, leading to mobilization of intracellular calcium. The Ang II-induced PGE2 and PGI2 syntheses were attenuated by [Sar1,Ile8]Ang II but not by [Sar1,Thr8]Ang II. Ang-(1-7)-induced PGE2 and PGI2 syntheses were not inhibited by either of these two classical antagonists. DuP 753, a subtype 1-selective Ang receptor antagonist, blocked the Ang II-induced release of PGE2 but not PGI2. In contrast, CGP 42112A, the subtype 2-selective antagonist, totally blocked the Ang II-induced PGI2 release and partially attenuated the PGE2 release. Ang-(1-7)-induced PGE2 and PGI2 release was not altered by DuP 753; however, CGP 42112A totally blocked the effects of Ang-(1-7) on PG stimulation. Calcium mobilization in response to Ang II was blocked by [Sar1,Thr8]Ang II, [Sar1,Ile8]Ang II, and DuP 753 but not by CGP 42112A. These data suggest that human astrocytes contain both Ang receptor subtypes. The subtype 1 Ang receptor participates both in the release of PGs and in the mobilization of calcium, whereas the subtype 2 receptor is coupled to the release of PGs only. In addition, PG release coupled to subtype 2 Ang II receptors occurs through a calcium-independent mechanism and responds uniquely to Ang-(1-7).

It has been shown that in vitro angiotensin II (Ang II) potently downregulates endothelin-1 (ET-1) binding sites. In this study, we investigated in vivo the interactions between the renin-angiotensin system and ET-1. Sprague-Dawley rats were pithed, ventilated, and diastolic blood pressure (DBP) was recorded. ET-1 (1 nmol/kg) induced a biphasic response: a transient hypotension followed by a sustained increase of DBP. Captopril (5 mg/kg, i.v.) or Sar1-Ile8-Ang II (10 ng/kg/min) did not affect ET-1 responses. In other experiments, DBP was increased by infusion of methoxamine (MTX: 10, 20, 25, 32.5 micrograms/kg/min) or Ang II (50, 100, 150, 200 ng/kg/min). ET-1-induced hypotension correlated with the level of DBP (r = 0.94) for both agonists. The elevation of DBP in response to ET-1 was also related to the vascular tone but was dose-dependently attenuated by Ang II infusion when compared with MTX. Conversely, infusion of ET-1 (0.1 nmol/kg/min) blunted the pressor response to Ang II (0.1 micrograms/kg) but not to MTX (50 micrograms/kg). These doses induced the same increase of DBP in pithed control rats. Similarly, increased plasma renin activity induced by chronic salt depletion (0% NaCl) in pithed rats provoked a shift to the right of the dose-response curves to Ang II and ET-1 but not to MTX. These results suggest an in vivo cross-desensitization between ET-1 and Ang II.

The purpose of this study was to compare the acute hypotensive efficacy of different types of inhibitor of the renin-angiotensin system. A renin inhibitor (RI), CGP 44,099 A, a converting enzyme inhibitor (CEI), enalaprilat, a peptidic angiotensin II (Ang II) antagonist, [Sar1, Ile8]Ang II (P-Ang IIA), and a nonpeptidic Ang II antagonist devoid of agonistic properties, 2-butyl-4-chloro-1- ([2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl)-5- (hydroxymethyl)imidazol (NP-Ang IIA), were administered intravenously to sodium-depleted rats (SDRs), renal hypertensive rats (two-kidney, one-clip) (RHRs), and spontaneously hypertensive rats (SHRs). The four compounds were all effective in lowering blood pressure (BP) in SDRs and RHRs. The maximum hypotensive response observed within 30 min of administration was similar for all four compounds (approximately 30 mm Hg in SDRs and 60 mm Hg in RHRs). In SHRs, the P-Ang IIA induced a pressor response whereas the RI, CEI, and NP-Ang IIA lowered BP to a similar extent (approximately 15 mm Hg). Pretreatment with the CEI completely prevented the hypotensive response to RI in SHRs, and vice versa. These observations indicate that the principal mechanism by which converting enzyme inhibitors lower BP after acute administration in these rat models is by inhibition of the formation of Ang II. The pressor response to the P-Ang IIA in SHRs is probably a consequence of its partial agonistic properties. Renin inhibitors and nonpeptidic Ang II antagonists, devoid of agonistic properties, promise to be effective antihypertensive agents similar to the CEIs.

Central cardiovascular effects of the sodium-potassium adenosine triphosphatase (Na+, K+-ATPase) inhibitor, ouabain, were investigated by injecting it intracerebroventricularly (ICV) using conscious Wistar rats. Ouabain, 0.1-10 micrograms injected ICV, produced dose-related pressor responses attaining peak elevations after about 5 min. To investigate the underlying mechanisms of these central pressor responses, angiotensin II blockers were injected ICV before the injections of ouabain. 1-Sar, 8-Ile angiotensin II (ang IIa), 50 micrograms, given 3 min before the ouabain, abolished the pressor responses to ouabain, 5 micrograms. Angiotensin I converting enzyme inhibitor (CEI, captopril), 100 micrograms, also significantly attenuated the pressor responses to ouabain. Since previous results with ICV injections of ouabain suggested that the pressor responses are mediated via a release of brain angiotension II, and the site of action of brain angiotensin II is believed to be the anteroventral third ventricle (AV3V) area of the brain, ICV injections of ouabain were repeated using rats whose AV3V areas had been destroyed electrically. The pressor responses were smaller in the AV3V lesioned rats than in sham-operated rats. The abdominal sympathetic nerve activity was recorded using three conscious, normotensive Wistar rats. ICV injections of ouabain, 5 micrograms, elicited pressor responses as described above and these were accompanied by a corresponding increase in the nerve firing, lasting for 5-7 min. These responses were again abolished by pretreatment with an angiotensin II antagonist. These results suggest that centrally administered ouabain elicits vasopressor responses which increase peripheral sympathetic nerve activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of angiotensin II (Ag-11) and 1-sar., 8-isoleu. angiotensin 11 (anti-Ag-11) on the membrane and mechanical properties of smooth muscle cells of the rat portal vein were investigated in three different age groups (6--8 weeks, immature rat; 3--5 months old, young rat and 13--15 months old, adult rat). Application of Ag-11 (10(-10) g/ml) did not depolarize the membrane, but did increase the spike frequency and potentiated the frequency and amplitude of twitch contraction. In a concentration of more than 10(-9) g/ml Ag-II, the membrane was depolarized and a phasic contracture was developed in three age groups. Depolarization of the membrane produced by Ag-II could be classified into two components, i.e. phasic and tonic depolarizations. In adult rats, Ag-II produced the highest amplitude of the depolarization in three age groups but tonic depolarization showed nearly the same amplitude of smooth muscle cell membrane to Ag-II increases with age up to 3--5 months and that an increased sensitivity is accompanied by a generation of desensitization. Tachyphylaxis to Ag-II was also observed by repetitive applications, but the appearance depended on the stimulus conditions. Anti-Ag-II, itself slightly increased the spike frequency and the amplitude of twitch contraction. However, under pretreatment with anti-Ag-II (10(-9) or 10(-7) g/ml), the actions of Ag-II on the electrical and mechanical activities were markedly suppressed in the three age groups. When the dose-response curve was obtained from the mechanical response produced by Ag-II, the relation shifted to the right in the presence of anti-Ag-II in all age groups. In the presence of 10(-7) g/ml anti-Ag-II, no contracture was evoked by application of 10(-6) g/ml Ag-II in three age groups. Anti-Ag-II seems to possess a higher affinity to the angiotensin receptor than does Ag-II.

We used very high doses of a competitive inhibitor of angiotensin II to investigate the role of the intrarenal renin-angiotensin system in the autoregulation of renal blood flow. Studies were carried out in dogs in which the renin and prostaglandin systems were suppressed. The results of our studies indicate that angiotensin II is not a prime mediator of the autoregulation of renal blood flow in response to reduced perfusion pressure.

1 The mechanism involved in catecholamine (CA) release from the cat adrenal gland in response to insulin hypoglycaemia was studied. In intact cats, hypoglycaemia induced an 11 fold increase in adrenomedullary CA secretion. 2 Acute bilateral nephrectomy nearly abolished the increased CA release from the adrenal gland during hypoglycaemia. 3 Infusion of Sar1-Ileu8-Angiotensin II (AII), a competitive AII antagonist, suppressed the adrenomedullary response to the insulin-induced hypoglycaemia. After termination of the antagonist infusion CA secretion from the adrenal medulla increased rapidly, reaching the same level as in insulin-treated cats. 4 Infusion of rabbit anti-angiotensin I antibodies suppressed CA release from the adrenal gland of hypoglycaemic cats. This effect was more prolonged than that of Sar1-Ileu8-AII. 5 These results indicate that CA release from the adrenal medulla of the cat in response to insulin-induced hypoglycaemia, is mediated through the renal reninangiotensin system. Since hypoglycaemia causes sympathetic stimulation through a central mechanism, angiotensin may act through the central nervous system.

The effect of a converting-enzyme inhibitor (captopril) was studied in nine conscious dehydrated Merino ewes. Captopril (4 mg I.V. over 40 min) caused significant decreases in mean arterial blood pressure (M.A.B.P.), renal vascular resistance (R.V.R.) and filtration fraction, and increases in urine flow (V), sodium excretion, glomerular filtration rate (G.F.R.), renal plasma flow, solute clearance (Cosm), solute-free water reabsorption (TC, H2O) and plasma renin activity (P.R.A.). None of these effects was observed when captopril was similarly administered to sheep pretreated with angiotensin II (AII) receptor blocker, 1-sarcosine-8-isoleucine-AII (sarileucin). It is concluded that the effects of captopril were probably not due to bradykinin potentiation but rather to decreased levels of circulating AII. The effect of sarileucin itself was complex. It effectively blocked the pressor response to administered AII, but it also had an AII-like effect indicated by a rise in R.V.R., and decreases in V, G.F.R., Cosm and TC, H2O. This apparent mixture of AII agonist and antagonist properties probably accounts for the absence of any change in M.A.B.P. or P.R.A. during sarileucin administration.

In order to evaluate the role of the renin-angiotensin system and the sympathetic nervous system in the maintenance of blood pressure in the sodium-depleted state, the changes of plasma renin activity (PRA), plasma aldosterone concentration (PAC) and plasma noradrenaline (PNA) were examined in unanesthetized dogs after the administration of furosemide. Furthermore, the role of the renin-angiotensin system in the increased sympathetic nerve activity induced by furosemide was assessed by using Sar1-Ile8-angiotensin II, an angiotensin II antagonist. When a dose of 0.8 mg/kg of furosemide was injected intravenously, 3 times every 15 minutes, PRA and PNA were significantly increased with a concomitant increase in PAC. Sar1-Ile8-angiotensin II induced a significant increase in PAC and a slight increase in PRA, while no changes were found in PNA and the mean blood pressure. The increase in PNA induced by furosemide was inhibited dose-dependently by Sar1-Ile8-angiotensin II, through PRA and PAC were further increased. There results suggest that an administration of furosemide induced the increase in PNA and the increase in PNA by furosemide might by mediated by the renin-angiotensin system.

1. The effects on phosphatidylinositol metabolism of three Ca(2+)-mobilizing glycogenolytic hormones, namely angiotensin, vasopressin and adrenaline, have been investigated by using rat hepatocytes. 2. All three hormones stimulate both phosphatidylinositol breakdown and the labelling of this lipid with (32)P. 3. The response to angiotensin occurs quickly, requires a high concentration of the hormone and is prevented by [1-sarcosine, 8-isoleucine]angiotensin, a specific angiotensin antagonist that does not prevent the responses to vasopressin and to adrenaline. This response therefore seems to be mediated by angiotensin-specific receptors. 4. [1-Deaminocysteine,2-phenylalanine,7-(3,4-didehydroproline),8-arginine] vasopressin, a vasopressin analogue with enhanced antidiuretic potency, is relatively ineffective at stimulating phosphatidylinositol metabolism. This suggests that the hepatic vasopressin receptors that stimulate phosphatidylinositol breakdown are different in their ligand selectivity from the antidiuretic vasopressin receptors that activate renal adenylate cyclase. 5. Incubation of hepatocytes with ionophore A23187, a bivalent-cation ionophore, neither mimicked nor appreciably changed the effects of vasopressin on phosphatidylinositol metabolism, suggesting that phosphatidylinositol breakdown is not controlled by changes in the cytosol Ca(2+) concentration. This conclusion was supported by the observation that hormonal stimulation of phosphatidylinositol breakdown and resynthesis persists in cells incubated for a substantial period in EGTA, although this treatment somewhat decreased the phosphatidylinositol response of the hepatocyte. The phosphatidylinositol response of the hepatocyte therefore appears not to be controlled by changes in cytosol [Ca(2+)], despite the fact that this ion is thought to be the second messenger by which the same hormones control glycogenolysis. 6. These results may be an indication that phosphatidylinositol breakdown is an integral reaction in the stimulus-response coupling sequence(s) that link(s) activation of alpha-adrenergic, vasopressin and angiotensin receptors to mobilization of Ca(2+) in the rat hepatocyte.

1. Electrical stimulation of the brachial nerves at 3 Hz (15 V, 0.2 ms), in sodium pentobarbitone-anaesthetized rats whose renal arterial pressure was held constant, elicited a 26% increase in systemic blood pressure, a 15% rise in heart rate, an 11% reduction in renal blood flow, did not alter glomerular filtration rate and significantly reduced absolute and fractional sodium excretions and urine flow by 44, 49 and 31%, respectively. 2. In a separate group of rats, brachial nerve stimulation at 3 Hz increased plasma renin activity approximately 2-fold, while in animals in which the brachial nerves were not stimulated plasma renin activity did not change. 3. Following inhibition of the renin-angiotensin system with captopril or sar-1-ile-8-angiotensin II, brachial nerve stimulation resulted in similar increases in systemic blood pressure and heart rate as in the animals with an intact renin-angiotensin system but, in captopril-infused rats, did not change renal haemodynamics or urine flow while absolute and fractional sodium excretions were reduced by 20 and 25%, respectively. In sar-1-ile-8-angiotensin II-infused animals, similar nerve stimulation decreased renal blood flow by 12%, glomerular filtration rate by 7% and absolute and fractional sodium excretions and urine flow by 25, 18 and 18%, respectively. These decreases in sodium and water output were significantly smaller than those observed in animals with an intact renin-angiotensin system. 4. Stimulation of the brachial nerves increased post-ganglionic efferent renal nerve activity by 20% and the magnitude of this response was unaffected following inhibition of the renin-angiotensin system. 5. The results show that low rates of brachial nerve stimulation in the rat can increase efferent renal nerve activity and result in an antinatriuresis and antidiuresis which is dependent on the presence of angiotensin II, and appears to be due to an action of angiotensin II at the level of the kidney.

Intracisternal injections of hypertonic NaCl elicited the pressor responses in urethane anesthetized spontaneously hypertensive and normotensive Wistar rats. The intracisternal pretreatment of 1-Sar-8-Ile-angiotensin II, angiotensin II analog, could abolish the pressor responses to intracisternal injections of 5% NaCl in urethane anesthetized spontaneously hypertensive rats, while basal blood pressure was not affected by these pretreatment. Both intracisternal and intravenous administration of captopril, an angiotensin I converting enzyme inhibitor, did not alter the pressor effect of hypertonic NaCl in normotensive rats. Basal blood pressure was lowered by intravenous injection of captopril. The involvement of angiotensin II in the pressor mechanism of hypertonic NaCl was confirmed by the enhanced pressor responses to intracisternal injections of 5% NaCl in urethane anesthetized rats pretreated intracisternally with angiotensin II. These findings suggest that angiotensin II itself could play an important role in the pressor responses to intracisternal injections of hypertonic NaCl without involving a converting enzyme system.

Among the various biological effects of angiotensin II (AII), both pressor activity and aldosterone stimulation appear to be mediated by functionally different receptors. With this in mind, we compared pressor and aldosterone-stimulating activities of AII with those of triprolyl [(Pro)3] AII and pentasarcosyl [(Sar)5] AII. In conscious male Wistar rats (Pro)3 AII and (Sar)5 AII produced 48 and 46% of the pressor activity of AII. After intravenous infusion (conscious unrestrained rats, 125 pmol/kg/min for 30 min), plasma aldosterone concentrations were not significantly different from those of control rats which were infused with saline. However, when the rats were infused with AII (125 pmol/kg/min for 30 min), plasma aldosterone concentrations increased significantly (1,306 +/- 80 pg/ml). This study indicates that (Pro)3 AII and (Sar)5 AII may prove to be useful tools to elucidate biological actions of AII.

Isoproterenol infusion (0.1 microgram/kg per min) into the renal artery of the cat induced an increase in plasma renin concentration (PRC) from 14.3 +/- 5.7 (mean +/- SE) ng angiotensin I/ml per hr to 56.8 +/- 7.7 after 70 minutes (P < 0.05) and an increase in catecholamine secretion rate from 38.7 +/- 6.0 ng/kg per 10 min to 180.0 +/- 40.0 after 70 minutes (P < 0.001). Intravenous infusion of the same dose of isoproterenol had no significant effect on adrenomedullary catecholamine secretion rate. Isoproterenol induced preferential norepinephrine release: the ratio of norepinephrine to epinephrine secretion changed from 11.5:23.7 during the control period to 130.0:40.1 70 minutes after the start of isoproterenol administration. Intrarenal infusion of propranolol (3.0 mg/kg per min) inhibited renal renin release and adrenal catecholamine secretion in response to intrarenal isoproterenol. Intravenous infusion (0.4 microgram/kg per min) of an angiotensin II antagonist [Sar1, Ileu8]angiotensin II abolished the catecholamine response to intrarenal isoproterenol infusion. It is suggested that intrarenal isoproterenol infusion stimulates renal renin release and angiotensin production which, in turn, stimulates a preferential secretion of adrenomedullary norepinephrine.

Acute effects of captopril (SQ 14 225) on blood pressure were investigated in pentobarbital anesthetized dogs. Intravenous captopril (0.1-3 mg/kg) caused reduction of blood pressure dose-independently, while dose-dependent attenuation of exogenous angiotensin I-induced pressor response and potentiation of bradykinin-induced reduction of blood pressure were observed wih the same doses of this agent. This acute decrease in blood pressure was partially inhibited by a pretreatment with any one of aprotinin, Sar1-Ile-8-angiotensin II and indomethacin. More significant inhibition of the blood pressure decrease was observed after the combined pretreatment with Sar1-Ile8-angiotensin II and indomethacin or that with all the three drugs, though no complete abolition of the blood pressure decrease was achieved. These results suggest that captopril may decrease blood pressure in anesthetized dogs through other mechanism(s) in addition to angiotensin converting enzyme inhibition, including the prostaglandin release probably from the kidney.

The effects of intravertebral artery infusions of [Sar1, Ile8] and [Sar1, Thr8] angiotensin II on the central nervous system were studied in furosemide-treated dogs anesthetized with alpha-chloralose. Acute administration of furosemide led to a significant increase in plasma renin activity, plasma noradrenaline levels and heart rate, and also to a slight rise of blood pressure. In the furosemide-treated dogs, intravertebral artery infusion of either angiotensin II antagonist (250 ng/Kg/min, for 30 min) suppressed the furosemide-induced increases in plasma noradrenaline, heart rate and arterial blood pressure. The effects of [Sar1, Thr8] angiotensin II on the last two parameters were more pronounced than those of [Sar1, Ile8] angiotensin II. Intravenous infusion of the same dose of each antagonist had little influence on the furosemide-induced increases in arterial blood pressure, heart rate and plasma noradrenaline levels. These results suggest that the central actions of angiotensin II contribute to the regulation of blood pressure through the sympathetic nervous system.

The renin-angiotensin-aldosterone system, electrolyte and water balance, body fluid, and neurogenic tone and reactivity of the vasculature were studied in hypertension induced in uninephrectomized rats by repeated injection of renin-rich kidney extract and 1% saline drinking. The control rats were injected with physiological saline. Various measurements were made in conscious rats on the 10th day of the treatment. As compared with the control, plasma renin concentration and serum sodium increased significantly, while plasma aldosterone and renal excretory function did not differ. Blood volume (BV) expressed as per body weight increased significantly, but absolute BV, absolute or body weight-related plasma volume and hematocrit were not significantly different. The hypotensive effect of 1-Sar-8-Ile-angiotensin II was negligible 12 hours after the preceding injection of kidney extract. It was small but significant 1 hour after the injection. Increase in water turn-over and fractional sodium excretion occurred during the development of hypertension. Spironolactone did not significantly modify the developmental course. We observed increased depressor response to hexamethonium and increased reactivities to noradrenaline and angiotensin II (A II); these response curves relatively resembled those of spontaneously hypertensive rats. Hypertensive vascular changes were seen in the kidney and heart by histology. Thus, it was suggested that a direct vascular action of A II played a partial role in this hypertensive process while aldosterone played little role. The significance of BV increase and possible contribution of A II's other actions were discussed.

1 Modest stimulation of the renal nerves in the anaesthetized unilaterally nephrectomized cat resulted in a 15% fall in renal blood flow, no change in glomerular filtration rate and significant falls in both the absolute and fractional rates of sodium excretion.2 The haemodynamic responses to nerve stimulation were not modified by angiotensin II blockade with 1-Sar, 8-Ala angiotensin II although the fall in absolute, but not fractional sodium excretion was significantly larger. In contrast, stimulation of renal nerves following administration of 1-Sar, 8-Ileangiotensin II caused a significant fall in glomerular filtration rate. The reductions in both absolute and fractional sodium were of the same magnitude as in the absence of drug.3 Both renal blood flow and glomerular filtration rate were autoregulated during the reduction of renal perfusion pressure and this was associated with reductions in both absolute and fractional sodium excretions.4 In the presence of 1-Sar, 8-Ala angiotensin II, the haemodynamic and sodium excretory responses to reductions in renal perfusion pressure were not significantly different from those recorded in the absence of drug. However, following administration of 1-Sar, 8-Ile angiotensin II, renal blood flow but not glomerular filtration rate, was autoregulated during reduction in renal perfusion pressure. The falls in absolute and fractional sodium excretions caused by this manoeuvre were of similar magnitude to those obtained in the absence of drug.5 The results obtained using the 1-Sar, 8-Ile angiotensin II are consistent with angiotensin II having an important intra-renal site of action to regulate glomerular filtration rate, possibly via an action at the efferent arteriole. Administration of 1-Sar, 8-Ala angiotensin II was without effect on the regulation of renal haemodynamics which it is suggested reflects a limitation in the use of this particular compound as an intrarenal angiotensin II antagonist.

We studied the effect of angiotensin II analogue (AII-A) and angiotensin I converting enzyme inhibitor (SQ 14,225) on blood pressure and the renin-angiotensin-aldosterone system in a patient with pseudo-Bartter's syndrome, who was a 26-year-old unmarried Japanese woman taking furosemide surreptitiously. The intravenous infusion of AII-A decreased blood pressure from 85/35 to 68/28 mmHg. This decrease in blood pressure was associated with an increment of plasma renin activity (PRA) and a decrement of plasma aldosterone concentration (PAC). Similarly, SQ 14,225 given orally decreased blood pressure to the same extent. An increment of PRA and a decrement of PAC were also observed. These results suggest that the renin-angiotensin system plays a considerable role in maintaining blood pressure in pseudo-Bartter's syndrome. Again, attention has to be paid to the possibility of surreptitious use of diuretics in an adult patient with persistent hypokalemic alkalosis, hyperactivity of the renin-angiotensin-aldosterone system and angiotensin II insensitivity simulating "true" Bartter's syndrome.

Prehypertensive rabbits with renal artery stenosis of 3 days' duration (one-kidney, one clip) are known to have increased pressor responses to norepinephrine and vasopressin; this pressor hyperresponsiveness is restored to normal by the angiotensin II (AII) antagonist, [ Sar1, Ile8 ] AII, even though plasma renin activity (PRA) and plasma AII concentrations are not elevated. In the present study, the cross-circulation of blood between conscious one-kidney, 3-day renal artery stenosis rabbits and conscious normal rabbits resulted in the transfer of pressor hyperresponsiveness to the normal rabbits, although both groups of rabbits had normal values for PRA. A similar cross-circulation of blood between one-kidney rabbits without renal artery stenosis and normal rabbits did not alter the pressor responsiveness of the normal rabbits to norepinephrine. It was concluded that a circulating humoral factor is involved in mediating pressor hyperresponsiveness in 3-day renal artery stenosis rabbits. To evaluate the interrelationship between AII and the hormonal hyperresponsiveness factor, an additional experiment was performed in which blood was cross-circulated between one-kidney, 3-day renal artery stenosis rabbits and normal rabbits, with the normal rabbits receiving [ Sar1, Ile8 ] AII immediately following cross-circulation. Administration of this AII antagonist to the normal rabbits prevented them from showing pressor hyperresponsiveness following the cross-circulation of blood. It is concluded that in this prehypertensive renal artery stenosis model the humoral hyperresponsiveness factor exerts its effect through AII mechanisms, rather than AII acting to increase the release or secretion of the hyperresponsiveness factor.

Many avian species demonstrate atherosclerosis and high blood pressure (BP) that are influenced by age, sex, diet, and environment, but show no arteriosclerosis in small vessels. Thus, we aimed to define neural and humoral control of BP in conscious, 32-wk-old female chickens, Gallus gallus. Mean aortic pressure (determined by chronically implanted catheter) was 137.6 +/- 2.0 mm Hg; heart rate was 295 +/- 4 beats/min. Plasma renin activity (PRA), measured by radioimmunoassay of fowl angiotensin I ([Asp1, Val5, Ser9]AI), and plasma angiotensinogen levels were 3.55 +/- 0.31 ng/ml/hr and 1229 +/- 66 ng/ml respectively. Repeated injection of propranolol (4 to 8 mg/kg/day, i.m.) decreased (p less than 0.01) the BP 19.1 +/- 3.0 mm Hg and heart rate 76 +/- 6 beats/min. Acute infusion of propranolol also markedly reduced BP and heart rate, and increased plasma levels of norepinephrine and epinephrine. SQ 14,225 (20 mg/kg/day) reduced BP (p less than 0.01), but BP returned towards original levels unless a higher dose was given. PRA increased 2- to 6-fold. BP also decreased 31.0 +/- 2.1 mm Hg after reserpine treatment, but not after [Sar1, Ile8]AII. These results suggest that in maintaining BP in fowl the beta-adrenergic function is important, whereas the renin-angiotensin system may not have a primary role.

We have attempted to clarify whether or not captopril and 1Sar-8Ile-angiotensin II could protect isoproterenol-induced facilitation of norepinephrine release in guinea pig pulmonary arteries loaded with 3H-norepinephrine. Angiotensin I at 1 nM and 30 nM isoproterenol similarly facilitated evoked release of 3H-norepinephrine at 1 Hz. Captopril at 1 microM and 1Sar-8Ile-angiotensin II at 10 nM completely prevented angiotensin I-induced facilitation, whereas these pretreatments produced no effect on isoproterenol-induced facilitation. Isoproterenol-induced facilitation of norepinephrine release does not primarily involve a local angiotensin II mechanism.