Effect of Salt Balance on the Renal and Hemodynamic Actions of Benazepril in Normal Men

Renal and hemodynamic effects of diet alone and of single oral doses of the nonsulphydryl angiotensin converting enzyme (ACE) inhibitor, benazepril (10 mg), were investigated in eight healthy volunteers under stable conditions of high salt intake (300 mmol NaCl/day) and low salt intake (10 mmol NaCl/day), in a double blind, placebo controlled study. There were no changes in blood pressure between the two dietary extremes either during the run-in period or once sodium balance had been achieved. Mean renal plasma flow was higher, by approximately 10% and renal vascular resistance lower by 15%, on high salt diet compared to low salt diet. Glomerular filtration rates were found to be similar irrespective of the state of salt balance. Both plasma urate concentration and plasma renin activity were significantly elevated in the low salt compared to high salt state. Benazepril caused a greater fall in blood pressure in the sodium depleted state. Significant increases in the mean renal plasma flow, in the order of 15-20%, were seen over 6 h postbenazepril when compared with placebo response, regardless of the level of salt intake. Glomerular filtration rate over the same period remained unaltered. Benazepril doubled the urinary excretion of sodium over the first 4 hours after dosing whilst on the low salt diet; the equivalent increase during salt loading was approximately 20%. These results suggest that benazepril may exert direct effects on renal tubular function additional to those achieved through ACE blockade.