Acute administration of captopril lowers the natriuretic and diuretic response to a loop diuretic in patients with chronic cardiac failure.

Angiotensin-converting enzyme inhibitors suppress plasma concentrations of the sodium retaining hormones angiotensin II and aldosterone. This action should potentiate the natriuretic and diuretic effects of loop diuretics. Some studies indicate, however, that the introduction of angiotensin-converting enzyme inhibitors for the treatment of cardiac failure is associated with transient weight gain and the development of oedema. We have compared the natriuretic and diuretic response to intravenous frusemide 40 mg alone with the natriuretic and diuretic response to intravenous frusemide 40 mg following the administration of a single dose of captopril in 12 supine male patients with stable chronic cardiac failure. Captopril lowered the 4 h diuretic response to frusemide from 1160 (60) to 685 (77) ml (P less than 0.05) and the natriuretic response from 120 (9.6) to 68 (11.7) mmol (P less than 0.05). Creatinine clearance fell after captopril from 91 (7.2) to 57 (7.7) ml min-1 (P less than 0.05). Systolic and diastolic blood pressures were lower after the administration of captopril but these changes were not significant. Plasma renin activity rose from 3.8 (1.04) to 12.34 (2.94) ng ml h-1 (P less than 0.05) and plasma angiotensin II was reduced from 24.9 (5.05) to 8.14 (1.8) pg ml-1 (P less than 0.05). Plasma aldosterone concentrations were not significantly lower following captopril. Angiotensin-converting enzyme inhibitors cause an acute fall in creatinine clearance which may reduce the effects of loop diuretics and attention must be paid to diuretic dosage when initiating angiotensin-converting enzyme inhibitors for the treatment of cardiac failure.