Exercise increases susceptibility of muscle glucose transport to activation by various stimuli

The insulin sensitivity of glucose transport in skeletal muscle is enhanced after exercise. In this study, stimulation of transport of the nonmetabolizable glucose analogue 3-O-methylglucose by the insulin-mimetic agents vanadate and H2O2 was markedly enhanced in rat epitrochlearis muscles 18 h after a bout of swimming. This increase in susceptibility of the glucose transport process in muscle to stimulation by insulin-mimetic agents that act beyond the insulin-binding step provides evidence that the increased insulin sensitivity results from an effect of exercise on a later step in the activation of glucose transport. Hypoxia and insulin appear to stimulate glucose transport by different pathways in muscle as evidenced by an additivity of their maximal effects. The effect of a submaximal hypoxic stimulus on muscle sugar transport was greatly amplified 3 h after exercise. This increase in susceptibility of glucose transport to stimulation by hypoxia after exercise suggests that the increased sensitivity is not limited to the insulin sensitive pathway. In contrast to exercise (i.e., swimming), in vitro muscle contractions did not result in an increase in sensitivity of muscle glucose transport to insulin, raising the possibility that a humoral factor is necessary for this effect.