Influence of angiotensin II (AII) and angiotensin I (AI) on renal renin synthesis and release

Angiotensin II type 1 receptor-mediated augmentation of urinary excretion of endogenous angiotensin II in Val5-angiotensin II-infused rats

Rats infused chronically with Val(5)-Angiotensin (Ang) II exhibit increased urinary excretion of endogenous Ile(5)-Ang II by the 12th day of infusion, suggesting the stimulation of endogenous Ang II formation by Val(5)-Ang II infusion. The present study determined the time course of increased urinary Ang II excretion and the effects of Ang II type 1 receptor blockade (candesartan, 2 mg/kg per day) on the urinary excretion rates of Ile(5)-Ang II in Val(5)-Ang II-infused (80 ng/min) rats. Ile(5)-Ang II was separated from Val(5)-Ang II by high-performance liquid chromatography and measured by radioimmunoassay. Systolic blood pressure increased progressively (215+/-2 mm Hg) in Val(5)-Ang II-infused rats (n=5), whereas the candesartan-treated group (n=6) remained normotensive (124+/-3 mm Hg). Candesartan treatment significantly increased the level of plasma Ile(5)-Ang II (24.0+/-7.6 versus 156.9+/-24.6 fmol/mL; P<0.01); in contrast, there was a markedly lower intrarenal Ile(5)-Ang II content (357.9+/-76.6 versus 21.1+/-2.8 fmol/g; P<0.01). Urinary Ile(5)-Ang II excretion rates were elevated by day 9 (2185.7+/-283.2 fmol/24 hours) in Val(5)-Ang II-infused rats but not in candesartan-treated rats (740.6+/-110.3 fmol/24 hours). Thus, Ang II type 1 receptor blockade prevents the increase in urinary excretion of endogenous Ang II in rats subjected to chronic Ang II infusion. These data indicate that the increased urinary excretion of endogenous Ang II in Val(5)-Ang II-infused rats is primarily attributed to Ang II type 1 receptor-dependent secretion into and/or de novo formation of Ang II within the tubular lumen.

Renal angiotensin II receptor regulation in two-kidney, one clip hypertensive rats: effect of ACE inhibition

Local renal and plasma renin-angiotensin systems (RAS) both play an important role in blood pressure regulation during the development of two-kidney, one clip Goldblatt hypertension (2K1C) through their vasoactive component, angiotensin II (Ang II). Our goal was to characterize glomerular and preglomerular vascular Ang II receptors during the different stages of development of hypertension in 2K1C rats (2-, 4-, 8-, and 16-weeks postoperative) using Ang II antagonists [Sar1,Ile8]-Ang II, losartan, and PD 123319 and their regulation after angiotensin-converting enzyme (ACE) inhibition by captopril. Competitive binding studies showed that the only Ang II receptor detected on both glomeruli and preglomerular vessels of all groups (2-, 4-, 8-, and 16-week 2K1C rats, control rats, and captopril-treated rats) was the Ang II type 1 receptor (AT1). Vascular AT1 receptor density (Bmax) was significantly lower in only the 16-week 2K1C group, whereas glomerular Bmax was significantly lower in 2K1C rats at 2-, 4-, and 8-weeks. Vascular and glomerular receptor densities were both significantly higher in captopril-treated rats than in nontreated rats. We therefore conclude that in 2K1C rats, Ang II receptors on preglomerular vessels and glomeruli are regulated differentially during the development of hypertension and after ACE inhibition. Our results suggest that glomerular Ang II receptors are regulated by systemic plasma Ang II levels, whereas vascular Ang II receptors are not. However, when renal and systemic RASs are both blocked, these receptors are upregulated but are no longer differentially regulated.

Renin release regulation during acute renin inhibition in normal volunteers

Blockade of the renin-angiotensin system by an angiotensin converting enzyme (ACE) inhibitor or an angiotensin II (Ang II) antagonist is accompanied by a reactive rise in renin release. This rise is generally attributed to interruption of the short feedback loop between Ang II and renin release. Similarly, after the administration of a renin inhibitor, the plasma concentrations of active and total renin are increased and plasma renin activity is suppressed. The aim of the present study was to investigate if a fall in the plasma Ang II level is the unique determinant of the rise in the active renin (AR) level that follows renin inhibition. Six normal male volunteers participated in three successive 240-minute experiments at weekly intervals according to a single-blind randomized Latin square design. For experiment 1, Ang II was infused at 2 ng/kg/min from 0 to 60 minutes and at 4 ng/kg/min from 60 to 120 minutes. For experiment 2, 0.3 mg/kg of the new potent renin inhibitor Ro 42-5892 was injected at 30 minutes followed by infusion at 0.1 mg/kg/hr from 30 to 240 minutes. For experiment 3, Ang II and Ro 42-5892 were administered simultaneously at the same doses as described above. The mean +/- SEM Ang II concentration increased from 10.2 +/- 1.6 to 33.7 +/- 11.2 pg/ml after infusion of exogenous peptide. It decreased from 9.5 +/- 0.9 to 1.4 +/- 0.3 pg/ml after the injection of Ro 42-5892 and increased from 15.6 +/- 2.9 to 37.1 +/- 11.8 pg/ml after the simultaneous infusion of both compounds.(ABSTRACT TRUNCATED AT 250 WORDS)