Effects of dopamine blockade on renal sodium excretion

The renal responses to a specific dopamine antagonist (cis-flupentixol) and its stereoisomer (trans-flupentixol), a weak dopamine antagonist, were examined during hydropenia and Ringer loading in anesthetized rats. During hydropenia glomerular filtration (GFR), absolute (UNaV), and fractional (FENa) sodium excretion rates were similar as were single-nephron filtration (SNGFR) and proximal tubular flow rate (VTF). After Ringer loading GFR, UNaV, and FENa increased in all groups, but the increments were less in the cis-flupentixol than in the control or trans-flupentixol group. SNGFR and VTF increased similarly in all groups. In another series of experiments Ringer loading was performed prior to drug administration. Perfusion pressure (PP) was decreased in trans-flupentixol rats by aortic constriction to control for cis-flupentixol-induced reduction in PP. UNAV and FENa were lower in the cis-flupentixol- than trans-flupentixol-treated rats at comparable PP and GFR. In conclusion, dopamine blockade attenuated the natriuresis of Ringer loading; the mechanism is uncertain but may be related to a tubular effect at a site beyond the proximal convoluted tubule and/or in deeper nephrons.