Effects of enalapril alone, and in combination with hydrochlorothiazide, on renin-angiotensin-aldosterone, renal function, salt and water excretion, and body fluid composition.

Enalapril is a new, oral, long-acting nonsulfhydral angiotensin converting enzyme inhibitor. Thirty-nine patients with primary hypertension were entered into a randomized, double-blind protocol to assess the efficacy of enalapril (10 to 20 mg bid), hydrochlorothiazide (25 to 50 mg bid), or combined drug therapy. Enalapril, either alone or in combination with hydrochlorothiazide, effectively controlled blood pressure. Enalapril monotherapy was associated with an increase in plasma renin activity and a decrease in angiotensin II concentration; in patients with an initial inulin clearance less than or equal to 80 mL/min/1.73 m2, inulin and para-aminohippurate clearances were markedly improved, without producing adverse effects on salt and water excretion or body fluid composition. Combination therapy was associated with a marked increase in plasma renin activity; however, only those patients with an initial inulin clearance less than or equal to 80 mL/min/1.73 m2 demonstrated suppression of angiotensin II concentration and marked improvement in inulin and para-aminohippurate clearances. These observations suggest that enalapril, either alone or in combination with a diuretic, has the potential to reverse renal function abnormalities encountered in the hypertensive state.