The Effect of Ouabain on Substrate Metabolism in the Isolated Perfused Rat Heart

The effect of ouabain (2, 5, and 10 μg/ml) on the uptake and oxidation of 5 mM glucose-U-14C and 0.4 mM palmitate-1-14C was determined in the isolated perfused rat heart. During 30-min perfusions, 5 and 10 μg/ml ouabain enhanced glucose uptake and 10 μg/ml also increased glucose oxidation. Palmitate uptake, oxidation, and incorporation into tissue lipids were unaffected by ouabain. The addition of glucose did not alter the lack of effect of ouabain on palmitate metabolism, but the presence of palmitate inhibited the stimulatory effect of ouabain on glucose uptake. The ouabain enhancement of glucose uptake was not associated with any change in glycerol release from the perfused heart, nor did ouabain increase the stimulated glucose utilization due to insulin. The concentrations of ouabain used in these experiments were shown to have an inotropic effect when the glycoside was added after 45 min of control perfusion. Thus, ouabain had no effect on palmitate metabolism. The enhancement of glucose uptake and oxidation was not due to an antilipolytic effect, nor did ouabain potentiate the effect of insulin on glucose transport. The ouabain effect on glucose utilization was associated with, but not necessarily a result of, increased contractility.