Angiotensin II inhibition with captopril on plasma ADH, PG synthesis, and renal function in humans

Using captopril (C), an angiotensin (ANG) I converting-enzyme inhibitor, to increase endogenous prostaglandins (PGs) and to decrease endogenous ANG II synthesis, we studied the relationship between endogenous ANG II, PG, and antidiuretic hormone (ADH) release in seven normal volunteers before (control study) and after inhibition of PG synthesis by a single dose of aspirin (ASA study). In the control study, following the administration of 100 mg of C, there was a significant increase of plasma PGE2, plasma-renin activity (PRA), and urinary PGE2 and 6-keto-PGF1 alpha and a decrease of plasma ADH. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were unaffected by C; urine output, fractional sodium excretion (FENa), and osmolal clearance (Cosmol) increased; and urinary osmolality (Uosmol) decreased significantly after C. In the ASA study PG were undetectable in plasma and significantly reduced in urine 1 h after aspirin and did not increase when C was added. Plasma ADH decreased and PRA increased, as in the control study, after C, whereas GFR, RPF, urine output, FENa, Cosmol, and Uosmol were unchanged. These results suggest that the effect of C on ADH release may be mediated, to a large extent, by a fall in endogenous circulating ANG II, since ADH decreased in the presence of both high or undetectable levels of PGE2. The results also suggest that the increase in PGE2 induced by C may precipitate the diuretic and natriuretic effects of acute C administration.