Effects of captopril on blood pressure, electrolytes, and certain hormones in hypertension.

Short-term hypertensive and hormonal effects of captopril were studied in 26 hypertensive patients. Blood pressure (BP) and heart rate were recorded in subjects in the supine position 1 hr before and 3 hr after an oral dose of 1 mg/kg. Urinary, plasma electrolytes, plasma renin activity (PRA), and plasma aldosterone (PA) were determined before and after the test. It was verified, in a preliminary investigation involving 5 patients, that a placebo did not alter the measured parameters. Captopril decreased mean arterial pressure (mean ABP +/- SD) from 128 +/- 2.5 to 108.5 +/- 2.6 mm Hg (p less than 0.001); the maximum decrease was between 30 and 180 min. No changes in heart rate or plasma electrolytes were noted. PRA increased after captopril from 2.29 +/- 0.96 to 3.13 +/- 1.25 and to 4.11 +/- 1.87 at 1 hr and 3 hr (p less than 0.05). There was a correlation between PRA in standing subjects before captopril and decrease in mean ABP (r = 0.59, p less than 0.01). The best correlation was between the decrease in mean ABP and the maximum increase in PRA after captopril (r = 0.69). A good correlation was found between mean ABP and PRA 3 hr after captopril (r = 0.62). Correlation coefficients between decrease in mean ABP and either precaptopril PA or decrease in PA were not significant. In 14 patients, captopril (5.1 +/- 0.61 mg/kg/day) for 4 mo induced the same decrease in mean ABP that was observed during the test. After short- and long-term captopril, mean ABP correlated (r = 0.76, p less than 0.01).