Antihypertensive action of captopril in angiotensin-salt hypertension

Captopril (SQ 14225), a converting enzyme inhibitor, significantly lowered the arterial pressure (AP) of rats with angiotensin-salt hypertension, a hypertensive state associated with sodium retention, volume expansion, and suppression of both renin and aldosterone secretion. While captopril was acting, there was no increase in sodium, potassium, or water excretion. Thus, the antihypertensive effect was not due to natriuresis or diuresis. Moreover, as the AP was lowered, there was no change in plasma renin concentrtion, the pulse rate was lowered, and the lack of potassium retention suggested minimal or no effect on aldosterone secretion. The mechanism of action of captopril in a sodium-volume-expanded, renin-aldosterone-suppressed state is unknown.