INTRARENAL DOPAMINE PARTICIPATION IN FRUSEMIDE DIURETIC AND NATRIURETIC RESPONSES TO FRUSEMIDE

1 Dopamine (DA) involvement in the renal response to frusemide was ana lysed using the isolated perfused rat kidney preparation. Endogenous D A levels were increased through the infusion of its precursor levodopa (LD) (0.5 or 1 mu M) whereas benserazide (50 or 100 mu M), an inhibit or of the enzyme L-dopa-decarboxylase, was used to decrease DA synthes is. 2 Frusemide administration (0.3-20 nmols) induced a dose-dependent increase in fractional excretion of water (FE H2O), sodium (FE Na+) a nd glucose (FEG). FE Na+ elicited by the diuretic was enhanced 30-40% by 0.5 mu M of LD (n = 5, P < 0.05), and 60-80% by LD 1 mu M (n = 5, P < 0.05). FE H2O produced by the diuretic was enlarged 80-100% by 0.5 mu M (n = 5, P = 0.05), and 130-170% by 1 mu M of LD (n = 5, P < 0.01) . The increase produced by both concentrations of LD on FEG was 200% f or the lowest dose of the diuretic (n = 5, P < 0.01), and 90% for the highest (n = 5, P < 0.05). 3 Benserazide (BZ) (100 mu M) decreased the F.E. Na+ induced by frusemide (n = 5, P < 0.05) by 32-42%, and comple tely abolished frusemide effects on FE H2O and FEG (n = 5) 4 In conclu sion, our results suggest that endogenous dopamine participates in the frusemide-induced diuresis and sodium excretion within the kidney, an d that the participation of extrarenal factors is not essential for th is effect. Dopamine may be involved in frusemide-induced inhibition of proximal sodium reabsorption.