Effect of angiotensin II and an angiotensin II inhibitor on renin secretion in the dog

This study examined the effect of angiotensin II (AII) and (Sar-1Gly-8) AII, a competitive inhibitor of AII, on renin release in anesthetized dogs. An intravenous infusion of AII (25 ng/kg per min) raised BP 24 mmHg and lowered plasma renin activity (PRA) from 18.8 plus or minus 2.8 to 6.2 plus or minus 1. 3 ng/ml per h (P smaller than .001). When the intravenous infusion of AII inhibitor (1.0 mug/kg per min) was superimposed on the AII infusion, PRA rose from 6.5 plus or minus 22 to 12.3 plus or minus 3.6 ng/ml per h (P smaller than .02). Renal hemodynamics, BP, and urinary sodium excretion (UNaV) reverted toward pre-AII control values. A small dose of AII inhibitor (0.1 mu/kg per min) was then infused into one renal artery in animals receiving the constant intravenous infusion of AII. Renin secretion rate (RSR) increased significantly, not only in the infused kidney, but also in the contralateral kidney. In the latter there were no changes in renal hemodynamics or UNaV, and RSR was unimpaired by denervation of that kidney. The results suggest that the AII inhibitor blocks both the vascular and the renin-suppressing actions of AII and that the latter effect is more susceptible to inhibition.