Insulin binding and sensitivity in rat skeletal muscle: effect of starvation

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Abstract
In contrast to adipose tissue and heart, the in vitro sensitivity of skeletal muscle to insulin is enhanced by starvation. To determine the basis for this, insulin binding and its ability to stimulate glucose metabolism were examined in the incubated rat soleus. In solei from 50 g rats, starvation for 48 h enhanced insulin binding by 50-100% at concentrations of 100 ng/ml or less. Starvation also resulted in higher basal and insulin-stimulated rates of glycogen synthesis, glycolysis and glucose uptake. The enhanced effect of insulin only occurred at concentrations < 50-75 ng/ml, in keeping with the increased binding of insulin in this concentration range. Under conditions in which binding at equilibrium was the same, glucose uptake was still higher in the starved group, suggesting that some postreceptor event may have been more sensitive to insulin. The in vitro sensitivity of rat skeletal muscle to insulin is enhanced by 48 h of starvation. This evidently is due at least partially to an increase in insulin binding at physiological concentrations.