Reduction of plasma and urinary vasopressin during treatment of severe hypertension by captopril.

Plasma concentrations and urinary excretion rate of vasopressin (VP) were examined in ten cases of severe hypertension before and during short-term treatment by Captopril (SQ 14225). Before Captopril, plasma and urinary VP were high (respectively 5.24 pmol/l and 68 pmol/day) and positively correlated to plasma renin activity (PRA) and plasma aldosterone (PA). The decline in blood pressure (mean -15%) after Captopril was correlated not only to initial PRA and PA values, but also to plasma (r = 0.89; P less than 0.001) and urinary (r = 0.78; P less than 0.01) VP values. The initial dose of Captopril (1 mg/kg) induced a rapid decrease in blood pressure whereas plasma VP did not rise and aldosterone decreased. At the eighth day of Captopril treatment (mean daily dose 6 +/- 1.5 mg/kg) the drop in blood pressure (-12%) and in aldosterone persisted together with a significant reduction in plasma (1.18 pmol/l; P less than 0.01) and urinary (25 pmol/day; P less than 0.01) VP. It is suggested that these sustained simultaneous reductions in the rates of secretion of vasopressin and aldosterone are both elements of the antihypertensive effect of Captopril.