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Thirteen patients were entered into a protocol to assess the safety and efficacy of enalapril (MK 421), 5 to 20 mg b.i.d., and hydrochlorothiazide, 50 to 100 mg daily, for the treatment of renovascular hypertension. Specifically monitored were the effects of therapy on blood pressure and pulse, renal function, and the renln-angiotensin-aldosterone axis. Enalapril and hydrochlorothia-zide therapy produced excellent control of blood pressure with no adverse side effects. After approximately 8 weeks of therapy, renal vascular resistance was decreased and no adverse effects on glomeru-lar filtration rate or renal blood flow were noted, except in one patient with a functional unilateral stenotic kidney. Patients receiving enalapril and hydrochlorothiazide showed stimulation of plasma renin activity and suppression of plasma angiotensin II, although the initial degree of suppression was not sustained in all patients during prolonged therapy. Although plasma aldosterone concentration was initially suppressed, the degree of suppression was not sustained. Nine patients have been followed for an additional 6 months; none have experienced further progression of renal disease, as assessed by repeated measurements of glomenilar filtration and effective renal plasma flow. These results suggest that combined enalapril and hydrochlorothiazide therapy is safe and effective in the medical management of renovascular hypertension and that blood pressure control may be achieved in the absence of sustained interruption of the renin-angiotensin-aldosterone system. (Hypertension 8: 290-297,1986) KEY WORDS • glomerular filtration aldosterone system renal plasma blood flow • renin-angiotensin-T HAT the converting enzyme inhibitors capto-pril 1-3 and enalapril (MK 421) 6 " 9 effectively lower blood pressure in patients with renovas-cular hypertension has been demonstrated repeatedly. The initial fall in arterial pressure appears to be proportional to the concurrent fall in plasma angiotensin II concentration for both drugs. '• 7 Since the renin-angio-tensin system plays a crucial part in the regulation of glomerular filtration rate when renal perfusion pressure is low, and short-term administration of a converting enzyme inhibitor destroys the integrity of this system , administration of a converting enzyme inhibitor to a patient with renovascular hypertension carries the risk of precipitating serious renal dysfunction. Indeed,

Thirty-nine hypertensive patients were entered into a randomized, double-blind protocol to assess the effects of enalapril (10–20 mg b.i.d.), or combined enalapril (10–20 mg b.i.d.) and hydrochlorothiazide (25–50 mg b.i.d.) therapy on renal function and hemodynamics. Enalapril, either alone or in combination with hydrochlorothiazide, effectively controlled blood pressure. In patients with an initial inulin clearance ≤ 80 ml/min/1.73 m², inulin and p-aminohippurate clearances were markedly improved toward normal following either drug therapy. The filtration fraction was either unchanged (monotherapy) or increased (combination therapy), suggesting a direct glomerular effect of angiotensin-converting enzyme inhibition. Renal vascular resistance was decreased in all patients. 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.