ABSTRACT
OBJECTIVE: We aimed to measure the serial (time related) concentrations of aldosterone and renin after a single dose of 25 mg of captopril in normotensive individuals. With these results, we aim to ascertain the best sampling times for future tests. DESIGN: Six normotensive subjects were studied under two different conditions--once in a supine position and once under normal (erect-position) activity. Each subject was given 25 mg of captopril and his serum aldosterone and renin concentrations measured at half hourly intervals for four hours. Simultaneous half hourly blood pressure measurements were also noted. RESULTS: All subjects showed suppression of aldosterone levels with ingestion of captopril, and in the supine position maximal suppression was consistently observed from the 3rd to the 4th hour after ingestion. When studied in the erect posture, although there was significant suppression, this was not sustained, and a paradoxical rise of aldosterone levels was seen after 2 hours. Renin activity measured during this study showed no consistent patterns. The renin levels were unchanged in almost 40 per cent of cases, and raised in about 60 per cent of cases. None of the subjects had symptomatic postural hypotension after 25 mg of captopril. CONCLUSIONS: The captopril suppression test is safe and effective in assessing the suppressibility of aldosterone and the period of maximal suppression is from the 3rd to the 4th hour after oral ingestion of captopril.