Effect of Sar1-Ileu8-angiotensin on renal prostaglandin E2 biosynthesis and excretion

To test the hypothesis that renal prostaglandin (PG) biosynthesis is regulated by angiotensin (AII), rabbits were given prolonged treatment with the AII analogue, Sar1-Ileu8AII (200 micrograms/kg/4 hr, subcutaneously), for 2 days during a low, normal, and high sodium intake. Sodium restriction augmented plasma renin activity (PRA), which was associated with a rise in basal renal PGE2 synthesis and urinary excretion, whereas sodium supplementation attenuated PRA with a decrease in renal PGE2 synthesis and urinary excretion. Sar1-Ileu8AII administration, with either a low, normal, or high salt intake, suppressed PRA. Sar1-Ileu8AII injection with a low sodium intake also suppressed renal PGE2 synthesis and excretion that was associated with a fall in blood pressure, suggesting an antagonistic action of this agent on vascular beds and renal PGE2 synthesis. On the other hand, with a high sodium intake Sar1-Ileu8-AII increased renal PGE2 synthesis and excretion as well as blood pressure, revealing an agonistic action of this compound under these conditions. The results suggest that exogenous AII analogue may act as an antagonist or agonist depending on sodium intake and endogenous AII levels, renal PGE2 synthesis is dependent on AII levels, either endogenously produced or exogenously administered (as an AII agonist), and the action of AII analogue on vascular beds and renal PGE2 synthesis does not appear to parallel its action on renin-AII feedback regulation at the juxtaglomerular cell especially under conditions of high sodium intake.