Muscle alpha-aminoisobutyric acid transport after exercise: enhanced stimulation by insulin

After exercise the ability of insulin to stimulate glucose transport and glycogen synthesis in rat skeletal muscle is markedly enhanced (25). The present study was designed to determine whether prior exercise augments the stimulation of other processes by insulin and, if so, whether this can be attributed to an increase in insulin binding to its receptor. Toward this end rats were run on a treadmill for 45 min at moderate intensity and the uptake of alpha-aminoisobutyric acid (AIB) by muscle was then assessed using the isolated perfused hindquarter preparation. Approximately 30 min after the cessation of exercise, both the sensitivity and responsiveness of insulin-stimulated AIB uptake were significantly enhanced in the soleus and the red portion of the gastrocnemius. As previously shown for glucose transport and glycogen synthesis, only small effects were observed in the white portion of the gastrocnemius, which unlike the other muscles was not depleted of glycogen during the run. Insulin-stimulated glucose utilization was also enhanced in the incubated soleus muscle of exercised rats; however, insulin binding to the soleus was not altered. These studies indicate that the ability of insulin to stimulate processes other than glucose transport and glycogen synthesis is enhanced in skeletal muscle after exercise and that this is not due to an alteration in insulin binding. The changes in insulin-stimulated AIB uptake and glucose metabolism after exercise are the reverse of those found in denervated and immobilized muscle and in both situations insulin binding is not altered. This suggests that a common factor(s) modulates the increase in insulin effect after exercise and the insulin resistance of disuse.