Adaptation of fat cells to exercise: response of glucose uptake and oxidation to insulin.

The purpose of this study was to determine whether exercise training alters the sensitivity and responsiveness to insulin of glucose uptake and oxidation in fat cells. Female rats were exercised by swimming 6 h/day, 5 days/wk for 12 wk. The swimmers' fat cells were smaller than those of sedentary controls of the same age and similar body weight. A larger amount of insulin was specifically bound by fat cells of the trained rats because of an increase in the number of insulin receptors. The rates of 2-deoxyglucose uptake and of glucose oxidation were higher in fat cells of trained compared with sedentary rats at all insulin concentrations. A maximal insulin stimulus resulted in rates of sugar uptake and oxidation that were about sixfold higher in trained than in sedentary rats' fat cells. This greater responsiveness to insulin could not be explained by the increase in insulin binding but appears to be mediated by adaptation/s) at a step(s) beyond the binding of insulin to its receptors. Our findings suggest that fat cells of exercise-trained animals are adapted for rapid replenishment of energy stores.