Urine Dilution and Concentration After Digoxin Infusion into the Renal Artery of Dogs (34898)

The present studies extend our observations of the effect of digoxin on renal concentrating capacity and, in addition, investigate its action on renal diluting capacity. Infusion of digoxin into a renal artery of dogs undergoing water diuresis resulted in increases in fractional urine flow (V/100 ml GFR) and fractional sodium clearance (C_Na/100 ml GFR) to levels which could not be accounted for simply by distal inhibition, suggesting that the glycoside suppressed proximal reabsorption as well. Furthermore, CH₂O was inhibited at any level of V/100 ml GFR examined. These effects of digoxin on T^C_H2O and C_H2O indicate that it inhibits sodium transport in the ascending limb of Henle's loop. In view of our previous demonstration that the digoxin inhibition of T^c_H2O is accompanied by significant depression of Na⁺, K⁺-ATPase activity from medullary renal tissue, the present experiments are further evidence that the enzyme plays a fundamental role in the mechanism of urine concentration and dilution.