Transmural distribution of glucose uptake in the rat heart: effects of mechanical work load, substrate supply and exercise.

Glucose uptake is greater in the subendocardial layer of a Langendorff-perfused rat heart than in the subepicardial layer during basal conditions and also under basal conditions in the rat in vivo. The increase of aortic pressure in vitro or physical exercise in vivo causes the disappearance of the transmural gradient in glucose uptake, as does also the elimination of the mechanical work load by potassium induced cardiac arrest. Co-infusion of alternative substrates (oleate, lactate or acetate) causes an overall inhibition of cardiac glucose uptake but does not affect its proportional regional uptake. The left ventricular work load seems thus to be the major determinant of the transmural distribution of the left ventricular glucose uptake. Chronic physical exercise results in the disappearance of the transmural gradient in glucose uptake measured in isolated perfused heart. This redistribution of glucose uptake may reflect differences in the adaptative response of various myocardial layers to a long-term intermittent increase in the cardiac work load.