CHANGES IN INSULIN-STIMULATED GLUCOSE-TRANSPORT AND GLUT-4 PROTEIN INRAT SKELETAL-MUSCLE AFTER TRAINING

After running training, which increased GLUT-4 protein content in rat skeletal muscle by <40% compared with control rats, the training effec t on insulin-stimulated maximal glucose transport (insulin responsiven ess) in skeletal muscle was short lived (24 h). A recent study reporte d that GLUT-4 protein content in rat epitrochlearis muscle increased d ramatically (similar to 2-fold) after swimming training (J.-M. Ren, C. F. Semenkovich, E. A. Gulve, J. Gao, and J. O. Holloszy. J. Biol. Che m. 269, 14396-14401, 1994). Because GLUT-I protein content is known to be closely related to skeletal muscle insulin responsiveness, we thou ght it possible that the training effect on insulin responsiveness may remain for >24 h after swimming training if GLUT-4 protein content de creases gradually from the relatively high level and still remains hig her than control level for >24 h after swimming training. Therefore, w e examined this possibility. Male Sprague-Dawley rats swam 2 h a day f or 5 days with a weight equal to 2% of body mass. Approximately 18, 42 , and 90 h after cessation of training, GLUT-I protein concentration a nd 2-[1,2-H-3]deoxy-D-glucose transport in the presence of a maximally stimulating concentration of insulin (2 mU/ml) were examined by using incubated epitrochlearis muscle preparation. Swimming training increa sed GLUT-4 protein concentration and insulin responsiveness by 87 and 85%, respectively, relative to age-matched controls when examined 18 h after training. Forty-two hours after training, GLUT-4 protein concen tration and insulin responsiveness were still higher by 52 and 51%, re spectively, in muscle from trained rats compared with control. GLUT-4 protein concentration and insulin responsiveness in trained muscle ret urned to sedentary control level within 90 h after training. We conclu de that 1) the change in insulin responsiveness during detraining is d irectly related to muscle GLUT-4 protein content, and 2) consequently, the greater the increase in GLUT-4 protein content that is induced by training, the longer an effect on insulin responsiveness persists aft er the training.