Effects of methyldopa on renal hemodynamics and tubular function.

To determine the effects of methyldopa on renal function, clearance studies were performed on hypertensive subjects during sustained steady-state water diuresis. The data reveal an acute fall in glomerular filtration rate and sodium clearance, whereas renal blood flow was unchanged. The antinatriuresis was the result of decreased filtration of sodium and possibly enhanced proximal tubular sodium reabsorption. These changes occurred before any demonstrable fall in systemic blood pressure; thus a direct effect of the drug on arteriolar resistance within the renal circulation is suggested. Chronic administration of methyldopa for 1 wk induced sustained reduction in blood pressure and resulted in the same changes in renal hemodynamics and sodium excretion noted after acute administration. These data suggest that methyldopa, like other antihypertensives, reduces glomerular filtration rate and increases sodium retention.