Natriuretic effect of calcium-channel blockers in hypertensives

This double-blind, randomized, crossover trial characterizes the acute natriuretic response to calcium-channel blockers (CCB) and investigates the role of hemodynamic and hormonal factors in mediating the natriuresis. Thirteen male subjects with essential hypertension received a single oral 20-mg dose of nifedipine or 120 mg of diltiazem. Renal functional and hemodynamic measurements were performed prior to and hourly for 4 hours following medication. Subjects then received these medications for 4 weeks at which time the above studies were repeated. Urinary sodium excretion increased within 60 minutes of CCB administration and the natriuresis was sustained for 4 hours. Cumulative sodium loss during the 4 hours of study was greater with nifedipine (43 +/- 12 mmol) than with diltiazem (18 +/- 6 mmol) (P less than 0.05). Despite natriuresis, urinary potassium excretion was decreased by both agents. Even though both drugs decreased the mean arterial pressure, inulin and paraaminohippurate (PAH) clearances were not altered. Plasma aldosterone concentrations decreased, plasma catecholamine concentrations increased, whereas plasma-renin activity was unchanged with both drugs. Body weight, glomerular filtration rate (GFR), renal plasma flow, plasma-renin activity, plasma aldosterone, and catecholamine concentrations were unchanged following 4 weeks of therapy. The acute natriuretic response after 4 weeks of therapy was similar to the response noted after the first dose. This study concludes that CCB are acutely natriuretic. Despite systemic hypotension, renal hemodynamics are unaltered during CCB therapy. Suppression of aldosterone as well as direct tubular effects of these drugs may mediate the natriuresis. Chronic therapy with CCB does not modify the acute natriuretic response to these agents.