RESUMEN
Direct effects of captopril on renal function were examined in isolated perfused rat kidneys. Captopril induced a significant increase in urinary volume and urinary sodium excretion (1.8- and 1.7-fold, respectively; both p less than 0.005), whereas urinary potassium excretion and renovascular resistance were not significantly changed. Because the perfusion medium lacks angiotensinogen, kininogen and aldosterone, the natriuretic action in perfused kidneys may not be related to its inhibitory action on angiotensin I converting enzyme or kininase II. Because the natriuresis was not accompanied by changes in renovascular resistance, it is suggested that captopril possesses a direct natriuretic action and that this property may partly explain the mechanism of captopril-induced natriuresis clinically observed.