1. In rabbits actively immunized against angiotensin II (AII), the appearance of anti-AII antibodies was associated with a rise in plasma renin activity (PRA), which did not occur in mock-immunized controls.
2. In conscious rabbits, infusion of the angiotensin inhibitor, Sar1-Ala8-angiotensin II (P-113), at rates of 0.055, 0.22 or 1.1 nmol min−1 kg−1 into the renal artery, caused dose-related increases in arterial PRA and renal arteriovenous PRA difference. Renal blood flow fell with the high dose, but not with the low or medium doses. A fall in arterial pressure, asynchronous with peak renin secretion, accompanied the medium- and high-dose infusions.
3. Intravenous infusion of inhibitor P-113, 5.5 nmol min−1 kg−1, into anaesthetized rats produced highly significant increases in PRA and plasma renin concentration without reduction in arterial pressure. There were no changes in PRA or plasma renin concentration in saline-infused control rats.
4. These findings suggest that AII blockade interrupts a negative feedback loop controlling renin secretion.