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 less than 50-75 ng/ml, in keeping with the increased binding of
insulin in this concentration range. On the other hand, 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. These studies confirm that the in vitro sensitivity of rat skeletal muscle to
insulin is enhanced by 48 h of
starvation. They suggest that this is due at least partially to an increase in
insulin binding at physiological concentrations.