Enalapril in hypertension with renal artery stenosis: long-term follow-up and effects on renal function.

Enalapril alone, 10-40 mg given once-daily, controlled systemic hypertension long-term (mean follow-up time 19 months) in patients with renal artery stenosis. Significant, but usually modest, increases in serum creatinine and urea were observed. No serious side-effects were seen. A highly significant reduction in peripheral plasma angiotensin II was maintained 24 h after the previous dose of enalapril. Plasma active renin concentration rose 20-fold with long-term enalapril, when the stenotic kidney showed significant secretion of inactive, as well as of active renin. With enalapril therapy, the contralateral kidney showed net extraction of active renin. In unilateral renal artery stenosis, circulation on the affected side is diminished and is mainly via the juxtamedullary nephrons, which become rich in associated renin. Important intrarenal compensatory actions of the renin-angiotensin system include support of glomerular filtration, enhancement of vasa recta-mediated counter-current exchange, sustained urea excretion and maintenance of renal artery pressure distal to the stenosis. These compensatory effects are lost with converting enzyme inhibition. Thus in patients who are candidates for operation, enalapril should usually be given for no more than one month before proceeding to corrective surgery, to allow maximum blood pressure reduction without endangering the stenotic kidney for too long. Enalapril can nevertheless be given effectively long-term in patients unsuitable for corrective surgery.