ROLE OF RENAL DOPAMINE D-1 RECEPTORS IN NATRIURESIS INDUCED BY CALCIUM-CHANNEL BLOCKERS

The direct tubular natriuretic effect of calcium channel blockers (CCBs) may be due to an interaction between CCBs and a renal tubular dopamine receptor. We therefore studied the effects of two chemically unrelated CCBs, diltiazem and isradipine, infused into the right renal artery of 5% saline-loaded anesthetized rats alone or in the presence of a D-1 antagonist, SKF-83742. Isradipine (0.03 mu g.kg(-1.)min(-1)) or diltiazem (20 but not 10 mu g.kg(-1.)min(-1)) alone produced an increase in urine flow and an approximate doubling of absolute and fractional sodium excretion, which was not seen in the left kidney or in the control animals (analysis of variance, Scheffe's test, P < 0.05). SKF-83742 alone given systemically or into the right renal artery did not affect these parameters but did block the actions of diltiazem or isradipine. There was nb change in mean arterial pressure, renal blood flow, or glomerular filtration rate in any of the experiments. In additional studies, we found that a combined infusion of dopamine (0.1 mu g.kg(-1.)min(-1)) and diltiazem (10 mu g.kg(-1.)min(-1)) (doses that by themselves did not alter renal function) produced a twofold or greater increase in urine flow and absolute and fractional sodium excretion; glomerular filtration rate was not significantly changed. Intrarenal arterial CCBs, without a change in renal hemodynamics, produce a natriuresis that is blocked by a D, antagonist. Concomitant administration of diltiazem and dopamine (each in subeffective doses when used alone) produces a synergistic effect. CCBs may exert their natriuretic effect by interacting with the renal D-1 receptor/signal transduction pathway.