摘要:

Angiotensin-(1-7) is a novel peptide of the renin-angiotensin system that counteracts the pressor and proliferative responses to angiotensin II. We now report that cultured bovine aortic endothelial cells contain a saturable, high-affinity [(125) I]angiotensin-(1-7) binding site with an affinity of 19.3 +/- 10.7 nmol/L and a density of 1351 +/- 710 fmol/mg protein. Angiotensin-(1-7) competed at a second lower-affinity site, with an IC50of 2.9 micro mol/L. The high-affinity angiotensin II receptor antagonist sarcosine1-isoleucine8-angiotensinII blocked [(125) I]angiotensin-(1-7) binding to bovine aortic endothelial cells at both a high- (IC50= 1.3 nmol/L) and a low-affinity (IC50= 6.2 micro mol/L) binding site. In contrast, D-alanine7-angiotensin-(1-7)completely blocked [(125) I]angiotensin-(1-7) binding, with an IC50of 19.8 nmol/L, suggesting that D-alanine7-angiotensin-(1-7) may selectively block responses to angiotensin-(1-7) in endothelial cells. Neither the AT1antagonist losartan nor the AT2antagonist PD 123319 exhibited significant competition for [(125) I]angiotensin-(1-7) binding to endothelial cells isolated from bovine aorta, in agreement with the absence of detectable mRNAs encoding typical angiotensin receptor subtypes 1 or 2 (AT1or AT2). Angiotensin II also competed for [(125) I]angiotensin-(1-7) binding to bovine aortic endothelial cells; however, the relative affinity was 13-fold lower than angiotensin-(1-7), suggesting a preference for angiotensin-(1-7) over angiotensin II. These results demonstrate that bovine aortic endothelial cells contain a unique non-AT1, non-AT2angiotensin receptor that preferentially binds angiotensin-(1-7). (Hypertension. 1997;29[part 2]:388-393.

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Recent studies have shown that angiotensin-(1-7) [Ang-(1-7)] interacts with kinins and augments bradykinin (BK)-induced vasodilator responses by an unknown mechanism. In this study, we evaluated whether the potentiation of the BK-induced vasodilation by Ang-(1-7) may be attributable to inhibition of BK metabolism, release of nitric oxide, or both. Isometric tension was measured in intact canine coronary artery rings suspended in organ chambers.125I-[Tyr0]-BK metabolism was determined in vascular rings by assessing the degradation of the peptide by high-performance liquid chromatography. Ang-(1-7) augmented the vasodilation induced by BK in a concentration-dependent manner in rings preconstricted with the thromboxane analog U46619. The EC50of BK (2.45 +/- 0.51 nmol/L versus 0.37 +/- 0.08 nmol/L) was shifted leftward by 6.6-fold in the presence of 2 micro mol/L concentration of Ang-(1-7). The response was specific for BK, since Ang-(1-7) did not augment the vasodilation induced by either acetylcholine (0.05 micro mol/L) or sodium nitroprusside (0.1 micro mol/L). Moreover, neither angiotensin I nor angiotensin II (Ang II) duplicated the augmented BK response of Ang-(1-7). Pretreatment of vascular rings with the nitric oxide synthase inhibitor, Nomega-nitro-L-arginine (L-NA; 100 micro mol/L) completely abolished the effects of Ang-(1-7) on BK-induced vasodilation whereas pretreatment with indomethacin (10 micro mol/L) was without effect. The potent specific BK B2receptor antagonist, Hoe 140, nearly abolished the BK and the Ang-(1-7) potentiated responses at 2 micro mol/L, whereas at a lower concentration (20 nmol/L) Hoe 140 shifted the response curve to the right for both Ang-(1-7) and vehicle; however, the augmented response to Ang-(1-7) persisted. Preincubation of vascular rings with 20 micro mol/L of the AT1(CV11974), AT2(PD123319), or nonselective (Sar1Thr8-Ang II) receptor antagonists had no significant effect on the Ang-(1-7)-enhanced vasodilator response to BK. Lisinopril (2 micro mol/L) significantly enhanced the BK-induced vasodilator response while at the same time it abolished the synergistic action of Ang-(1-7) on BK. In addition, pretreatment with 2 micro mol/L Ang-(1-7) significantly inhibited the degradation of125I-[Tyr0]-BK and the appearance of the BK-(1-7) and BK-(1-5) metabolites in coronary vascular rings. Ang-(1-7) inhibited purified canine angiotensin converting enzyme activity with an IC50of 0.65 micro mol/L. In conclusion, Ang-(1-7) acts as a local synergistic modulator of kinin-induced vasodilation by inhibiting angiotensin converting enzyme and releasing nitric oxide. (Hypertension. 1997;29[part 2]:394-400.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Angiotensin II stimulates secretion of corticosteroids and ouabain-like activity from adrenocortical cells. Distinct adrenocortical angiotensin II receptor subtypes (AT1, AT2) have been described, and the present studies investigated their roles in steroid secretion. Using primary bovine adrenocortical cell cultures under serum free conditions, angiotensin II stimulated the secretions of aldosterone, cortisol, and endogenous ouabain as verified by high-performance chromatography. The dose-response curves for stimulated steroid secretion were parallel with unitary slopes while the half-maximally effective concentrations of angiotensin II were 0.31 to 0.38 nmol/L for secretions of aldosterone and cortisol and 2.3 nmol/L for endogenous ouabain. The nonselective mammalian antagonist (Sar1-Ile8) angiotensin II blocked stimulated secretion of all three steroids without affecting basal output. In the presence of the AT1antagonist DuP753, angiotensin II-stimulated secretions of aldosterone and cortisol were blocked while secretion of endogenous ouabain was unaffected. In the presence of the AT (2) antagonist PD123319, both basal and angiotensin II-stimulated secretions of aldosterone and cortisol were normal while stimulated secretion of endogenous ouabain was inhibited. The secretion of endogenous ouabain was activated maximally by the AT2agonist CGP42112 under conditions in which aldosterone secretion was unaffected. These results demonstrate that AT2receptors stimulate secretion of endogenous ouabain from bovine adrenocortical cells. The specificity of AT1and AT2receptor stimulation indicates that separate signaling mechanisms having minimal cross talk control the adrenocortical secretions of corticosteroids and cardiac-active steroids. Adrenocortical AT2receptors may be important in the adaptation to low salt diets and other conditions in which angiotensin II is increased. (Hypertension. 1997;29[part 2]:401-407.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

To investigate the role of the renin-angiotensin system in the regulation of adrenal growth in deoxycorticosterone (DOC)-salt hypertensive rats, and the adrenal gene expression of angiotensin AT1and AT2receptors, three groups of uninephrectomized rats + DOC pellet + 0.9% NaCl were given water (DOC), losartan (DOC-L), or ramipril (DOC-R) by gavage. Controls had sham surgery and water gavage. Tail-cuff systolic and mean intra-arterial blood pressures were significantly higher in the three DOC groups than in controls and not different among the groups. Adrenal weight of DOC was slightly but not significantly greater than that of controls, while those of DOC-L and DOC-R were greater than that of controls (P < .01). Northern blots showed that AT1and AT2gene expression was significantly reduced in DOC (by 33% and 60%), while that of AT1(but not AT2) was significantly reduced further (versus control and DOC) in DOC-L and DOC-R. There were negative correlations between adrenal weight and AT1(r = -.80, P < .0001) or AT2(r = -.60, P < .005). We conclude that DOC-salt hypertension downregulates adrenal AT1and AT2gene expression by different mechanisms. Removal of the effects of angiotensin by losartan or ramipril downregulates AT1further and promotes adrenal growth, indicating the presence of an AT1-mediated growth-inhibitory action of angiotensin II on the adrenal gland. These observations constitute an additional example of a growth-inhibitory role for the AT1receptor, opposite to its more common growth-promoting actions in other organs and tissues. (Hypertension. 1997;29[part 2]:408-413.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

To understand the molecular mechanisms of cellular signaling of atrial natriuretic peptide (ANP), we have studied its effect on the enzymatic activity of endogenous and overexpressed protein kinase C (PKC) in rat thoracic aortic vascular smooth muscle (RTASM) cells. Angiotensin II (ANG II), endothelin-1 (ET-1), and 12-O-tetradecanoylphorbol 13-acetate (TPA) stimulated fourfold to fivefold PKC activity in PKC-alpha cDNA-transfected RTASM cells. However, pretreatment of these cells with ANP significantly inhibited the agonist-stimulated PKC activity in a dose-dependent manner. The inhibitory effect of ANP was more effective if cells were transfected with both PKC-alpha and guanylyl cyclase-A/atrial natriuretic peptide receptor (Npra) cDNAs. The agonist-stimulated PKC activity was also inhibited if RTASM cells were pretreated with cGMP analog 8-bromo-cGMP; however, the treatment of cells with a cAMP analog, dibutyryl-cAMP, did not show any discernible effect. The pretreatment of cells with Npra antagonist A-71915, significantly blocked the production of cGMP as well as the inhibitory effect of ANP on PKC activity. To further examine whether the antagonistic action of ANP and 8-bromo-cGMP on agonist-stimulated PKC activity were mediated through cGMP-dependent protein kinase (PKG), cells were treated with ANP or 8-bromo-cGMP and activators of PKC in the presence of KT-5823, a specific inhibitor of PKG. The treatment of cells with KT-5823 significantly attenuated the inhibitory effects of both ANP and 8-bromo-cGMP on agonist-stimulated PKC activity. The results from these studies provide strong evidence that ANP antagonizes the activation of PKC in RTASM cells, involving guanylyl cyclase-A receptor Npra and second messenger cGMP. Our data further support the notion that ANP acts as a negative mediator of signaling cross-talks between Npra and PKC in a cGMP-dependent manner, probably involving cGMP-dependent protein kinase in this process. (Hypertension. 1997;29[part 2]:414-421.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

A functional impairment in vasodilator tone may be important in the pathogenesis and/or maintenance of elevated peripheral vascular resistance in hypertension. Previous studies of hypertensive subjects have demonstrated impaired beta-adrenergic-mediated vasodilation paralleling a reduction in lymphocyte beta-adrenergic-stimulated adenylyl cyclase activity. We have suggested that this impairment is related to a defect in G-protein function. To determine whether this defect alters the coupling between the G-protein complex and adenylyl cyclase, we performed [(3) H]forskolin binding studies in lymphocytes from hypertensive subjects, older normotensive subjects, and younger normotensive control subjects. Maximal specific [(3) H]forskolin binding was used as an index of adenylyl cyclase binding sites. Gpp(NH)p-, NaF/AlCl3-, and isoproterenol-stimulated binding were used as indices of G-protein/adenylyl cyclase coupling. In the absence of other stimulators, maximal [(3) H]forskolin binding was not significantly different among groups. However, both Gpp(NH)p- and isoproterenol-stimulated [(3) H]forskolin binding were significantly decreased in lymphocytes from hypertensive subjects. Overall, Gpp(NH)p- and isoproterenol-stimulated [(3) H]forskolin binding were significantly inversely correlated with blood pressure. No differences in NaF/AlCl3-stimulated [(3) H]forskolin binding were detected between groups. These studies indicate that G-protein/adenylyl cyclase coupling is impaired in lymphocytes from younger hypertensive subjects and may contribute to the blood pressure-related defect in beta-adrenoceptor-stimulated adenylyl cyclase activity. (Hypertension. 1997;29[part 2]:422-427.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

We developed a model of spontaneously high human renin hypertension in the rat by producing two transgenic strains, one for human angiotensinogen with the endogenous promoter and one for human renin with the endogenous promoter. Neither transgenic strain was hypertensive. These strains were then crossed, producing a double transgenic strain. The double transgenic rats, both males and females, developed severe hypertension (mean systolic pressure, 200 mm Hg) and died after a mean of 55 days if untreated. The rats had a human plasma renin concentration of 269 +/- 381 (+/- SD) ng angiotensin I (Ang I)/mL per hour, plasma renin activity of 177 +/- 176 ng Ang I/mL per hour, rat angiotensinogen concentration of 1.49 +/- 1 micro gram Ang I/mL, and human angiotensinogen concentration of 78 +/- 39 micro gram Ang I/mL (n = 49). Control rats had plasma renin activity of 3.7 +/- 3.9 ng Ang I/mL per hour and rat angiotensinogen of 1.32 +/- 0.16 micro gram Ang I/mL. Angiotensinogen transgene expression by RNase protection assay was ubiquitously present but most prominent in liver. Renin transgene expression was high in kidney but absent in liver. The rats featured severe cardiac hypertrophy, with increased cross section of cardiomyocytes but little myocardial fibrosis. The kidneys showed atrophic tubules, thickened vessel walls, and increased interstitium. Both the angiotensin-converting enzyme inhibitor lisinopril and the specific human renin inhibitor remikiren lowered blood pressure to normal values. Double transgenic mice have been developed that exhibit features quite similar to those described here; their gene expressions are similar. The specificity of rodent and human renin is similarly documented. Although many elegant physiological studies can now be done in mice, rats nevertheless offer flexibility, particularly in terms of detailed cardiac and renal physiology and pharmacology. We conclude that this double transgenic strain will facilitate simultaneous investigation of genetic and pathophysiological aspects of renin-induced hypertension. The fact that human renin can be studied in the rat is a unique feature of this model. (Hypertension. 1997;29[part 2]:428-434.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Angiotensin II, a constrictor and mitogen of vascular smooth muscle cells, affects the release of endothelium-derived factors such as nitric oxide or endothelin-1. This study investigated the influence of endothelin-1, using the selective endothelin A receptor antagonist LU135252, on blood pressure and endothelial function in angiotensin II-induced hypertension in the rat. Two weeks of angiotensin II administration (200 ng/kg per minute) increased systolic blood pressure (+35 +/- 5 mm Hg; tail-cuff method) compared with placebo (P < .05). LU135252 alone did not affect systolic pressure but lowered the angiotensin II-induced pressure increase (P < .05). In isolated aortic rings, endothelium-dependent relaxations to acetylcholine were reduced in the angiotensin II group (P < .05 versus placebo) and improved by concomitant chronic LU135252 treatment (P < .05 versus angiotensin II). Blood pressure elevation strongly correlated with impaired endothelium-dependent relaxations to acetylcholine (r = -.967). LU135252 did not affect endothelium-independent relaxations to sodium nitroprusside, which were diminished after angiotensin II treatment (P <.05). In quiescent rings, chronic angiotensin II administration enhanced endothelium-dependent contractions to acetylcholine, which were reduced by LU135252 (P < .05). Impaired contractions to endothelin-1 and norepinephrine in the angiotensin II group were normalized after treatment with LU135252 (P < .05). Thus, chronic therapy with LU135252 partially prevents angiotensin II-induced hypertension and the alternations of the endothelial function observed in this experimental model. (Hypertension. 1997;29[part 2]:435-441.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The objective of this study was to determine the contribution of renal nerves to the enhanced afferent arteriolar reactivity observed in angiotensin II (Ang II)-induced hypertension. Uninephrectomized Sprague-Dawley rats were divided into four groups: sham rats, renal-denervated rats, Ang II-infused (at 40 ng/min for 13 days) rats, and Ang II-infused + renal-denervated rats. With the use of an implanted arterial catheter, mean arterial pressure (MAP) was monitored in conscious rats. Ang II infusion resulted in a progressive increase in MAP from 98 +/- 1 (day 0) to 166 +/- 7 mm Hg (day 13). This increase in MAP was attenuated in denervated rats and averaged 136 +/- 3 mm Hg on day 13. Kidneys were harvested on day 13 for microcirculatory experiments or measurement of intrarenal Ang II levels. Basal afferent arteriolar diameter was similar in all groups, and group averages ranged from 19.6 to 20.7 micro meter. Chronic Ang II infusion increased intrarenal Ang II levels. Renal denervation did not alter this effect. Increasing perfusion pressure from 100 to 160 mm Hg reduced afferent arteriolar diameter significantly by 11.2 +/- 0.6% in the sham group and by a similar degree in the remaining three groups. Superfusion with Ang II (10 nmol/L) reduced afferent arteriolar diameter by 34.3 +/- 2.0% in the sham group. This response was enhanced in Ang II-infused (62.3 +/- 3.4%) but not in renal-denervated or Ang II-infused + renal-denervated rats. Additionally, the enhanced afferent arteriolar reactivity to Ang II was not influenced by adrenergic receptor blockade. The afferent arteriolar response to norepinephrine was enhanced in renal-denervated, Ang II-infused, and Ang II-infused + renal-denervated rats compared with sham controls. Administration of the calcium ionophore A23187 decreased afferent arteriolar diameter similarly in all four groups. These results indicate that renal nerves contribute to the development of hypertension and to the enhanced afferent arteriolar responsiveness to Ang II elicited by chronic Ang II infusion. (Hypertension. 1997;29[part 2]:442-449.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The hypothesis that endogenous angiotensin II (Ang II) chronically supports baroreflex control of lumbar sympathetic nerve activity (LSNA) and heart rate (HR) via AT1 but not AT2 receptors was tested in conscious, normotensive rats. Rats were fed either a sodium deficient diet (LS) to increase circulating Ang II or a high-sodium diet (HS) for 2 to 3 weeks. One to two days after surgery to implant catheters and nerve electrodes, baroreflex curves were produced before and 40 minutes after intravenous administration of the AT1 antagonist losartan (10 mg/kg) or the AT2 antagonist PD123319 (500 micro gram/kg + 50 micro gram [center dot] kg-1[center dot] min-1). Mean arterial pressure (MAP) after losartan was maintained at basal levels with methoxamine. Forty minutes after losartan in LS rats, LSNA (46 +/- 5 to 22 +/- 1% max) and HR (414 +/- 7 to 387 +/- 8 bpm) were decreased (P < .05). Losartan decreased reflex control of LSNA more in LS than in HS rats (P < .05), as indicated by reductions in maximum LSNA (98 +/- 2 to 78 +/- 3% max) and minimum LSNA (42 +/- 5 to 21 +/- 5% max). Losartan also shifted reflex control of LSNA to a lower pressure in both groups, but the effect was larger in LS rats (-21 +/- 3 [LS] versus -9 +/- 2 [HS] mm Hg at basal LSNA; P < .05). Maximum gain was unaltered in either group. Similarly, losartan reduced maximum HR (534 +/- 6 to 495 +/- 9 bpm) and shifted the HR curve leftward (114 +/- 5 to 105 +/- 4 mm Hg) in LS but not in HS rats. In general, no changes were observed in MAP or baroreflex control of LSNA and HR after PD123319 in LS rats. These results suggest that in conscious, normotensive LS rats, endogenous Ang II supports LSNA and HR over a wide MAP range via AT1 but not AT2 receptors. (Hypertension. 1997;29[part 2]:450-457.)

ISSN:0194-911X    

出版商:OVID    

年代:1997

数据来源: OVID