Utilization of C 14 -labeled Glucose by Cardiac Muscle Treated with a Cardiac Glycoside

Abstract

Ouabain in a final concn. of 5x10-7 [image] was added simultaneously with CH-labeled glucose to slices of dog myocardium respiring in substrate-free medium. The C14O2 evolved in oxidation of the sugar was measured and compared with the CO2, whence it was concluded that the rate of glucose oxidation was doubled although stimulation of respiration by the cardiac glycoside was not accompanied by a greater uptake of glucose. Actually somewhat less glucose was taken up than in absence of the drug. Lactic acid production by the cardiac slices was greatly reduced by ouabain in the expt. Since the author found previously that in the presence of pyruvate, which increases rate of O2 consumption of cardiac slices to the level attained following addition of a cardiac glycoside in glucose or in lactate, the drug causes no further increase in metabolism, he infers that it exerts its effect by accelerating formation of pyruvate from glucose and lactate. No attempt is made to relate the present findings to an explanation of the action of the cardiac glycosides on cardiac function.