Effect of Ouabain and Acetazolamide on Proximal Tubular Transport in Dogs

Abstract

Local application of ouabain in high doses may stop all tubular electrolyte transport. Ouabain administered in vivo in a dose inhibiting 80% of renal Na/K-ATPase activity, reduces transcellular NaCl reabsorption by 40–50%. (1). A similar response is obtained by ethacrynic acid (3 mg/kg bwt) which selectively inhibits transcellular NaCl reabsorption without affecting bicarbonate and phosphate reabsorption (2). The purpose of the present study in volume-expanded, anesthetized dogs was to examine if ouabain during continuous ethacrynic acid infusion exerts any effect on lactate, phosphate and bicarbonate reabsorption. These anions are transported together with sodium mainly in the proximal tubules. In one series of experiments, acetazolamide, a potent inhibitor of NaHCO3 reabsorption and associated NaCl reabsorption in the proximal tubules (3), was administered after ouabain. In a second series the order of administration was reversed. In all ten dogs plasma concentrations of lactate, phosphate and bicarbonate were raised to 9 ±2, 2.4 ±0.3 and 31 ±1 mM respectively.