Muscle Glucose Metabolism following Exercise in the Rat

Abstract

A B S T R A C T Muscle glycogen stores are depleted during exercise and are rapidly repleted during the recovery period. To investigate the mechanism for this phenomenon, untrained male rats were run for 45 min on a motor-driven treadmill and the ability of their muscles to utilize glucose was then assessed during perfusion of their isolated hindquarters. Glucose utilization by the hindquarter was the same in exercised and control rats perfused in the absence of added insulin; however, when insulin (30-40,000 MU/ml) was added to the perfusate, glucose utilization was greater after exercise. Prior exercise lowered both, the concentration of insulin that half-maximally stimulated glucose utilization (exercise, 150 ,U/ml; control, 480 ,gU/ml) and modestly increased its maximum effect.The increase in insulin sensitivity persisted for 4 h following exercise, but was not present after 24 h. The rate-limiting step in glucose utilization enhanced by prior exercise appeared to be glucose transport across the cell membrane, as in neither control nor exercised rats did free glucose accumulate in the muscle cell.Following exercise, the ability of insulin to stimulate the release of lactate into the perfusate was unaltered; however its ability to stimulate the incorporation of ['4C]glucose into glycogen in certain muscles was enhanced. Thus at a concentration of 75 AU/ml insulin stimulated glycogen synthesis eightfold more in the fast-twitch red fibers of the red gastrocnemius than it did in the same muscle of nonexercised rats. In contrast, insulin only minimally increased glycogen synthesis in the fast-twitch white fibers of the gastrocnemius, which were not glycogen-depleted. The uptake of 2-deoxyglucose by these muscles followed a similar pattern suggesting that glucose transport was also differentially enhanced. Prior exercise did not enhance

Acute exercise increases insulin sensitivity in adult sheep: a new preclinical model

“…This is consistent with previous reports of increased whole body or skeletal muscle insulin sensitivity persisting for 4 -48 h after a single bout of exercise in humans (34,46,54) and 4 -48 h after acute exercise in rodents (8,18,44). This is the first report of exercise-induced increases in insulin sensitivity in a nonhuman large animal.…”

“…Previous studies in humans and rodents have reported increased insulin sensitivity after either higher-intensity or longer-duration acute exercise protocols than used in the present study (3,8,15,19,23,34,43,44,54). The exercise intensity achieved in the present study by sheep in the intensive exercise test (30 min, 8% slope, 4 -4.4 km/h) is probably ϳ50 -60% of V O 2max , based on studies in pregnant sheep (26).…”

“…Importantly, a single bout of exercise also increases the insulin sensitivity of glucose uptake during the following 4 -48 h in healthy humans (34,46,52,54,55). Similar effects have been demonstrated in rodents, where an acute exercise bout increases in vitro insulin-stimulated glucose uptake in mouse muscle 85 min after exercise (18) and in rat muscle collected 3-16 h after a single bout of exercise (8,15,19,43,44). Available evidence from studies in humans and rodents suggests that acute exercise, like exercise training, increases insulin sensitivity without changes in proximal insulin signaling (reviewed in Ref.…”

Brain-derived neurotrophic factor is produced by skeletal muscle cells in response to contraction and enhances fat oxidation via activation of AMP-activated protein kinase

“…Of note, exercise is associated with increased insulin-stimulated glucose uptake in the immediate postexercise period [2,3], while chronic physical activity enhances insulin sensitivity [4]. We have recently identified skeletal muscle as a cytokine-producing organ, demonstrating that the metabolic and physiological effects of exercise may also be mediated by skeletal muscle-derived humoral factors [5,6].…”

Prior exercise increases phosphorylation of Akt substrate of 160 kDa (AS160) in rat skeletal muscle

“…The insulinindependent effect is evident during and shortly after exercise, but it reverses relatively rapidly, with most of the effect typically lost ϳ3-4 h postexercise in rat muscle (10,43). As the exercise effect on insulin-independent glucose transport subsides, glucose transport in the presence of a physiological insulin concentration can be substantially elevated (9,10,32,43).…”