title: Voluntary exercise training enhances glucose transport in muscle stimulated by insulin-like growth factor I.
abstract: Skeletal muscle glucose transport can be regulated by hormonal factors such as insulin and insulin-like growth factor I (IGF-I). Although it is well established that exercise training increases insulin action on muscle glucose transport, it is currently unknown whether exercise training leads to an enhancement of IGF-I-stimulated glucose transport in skeletal muscle. Therefore, we measured glucose transport activity [by using 2-deoxy-D-glucose glucose (2-DG) uptake] in the isolated rat epitrochlearis muscle stimulated by submaximally and maximally effective concentrations of insulin (0.2 and 13.3 nM) or IGF-I (5 and 50 nM) after 1, 2, and 3 wk of voluntary wheel running (WR). After 1 wk of WR, both submaximal and maximal insulin-stimulated 2-DG uptake rates were significantly (P < 0.05) enhanced (43 and 31%) compared with those of sedentary controls, and these variables were further increased after 2 (86 and 57%) and 3 wk (71 and 70%) of WR. Submaximal and maximal IGF-I-stimulated 2-DG uptake rates were significantly enhanced after 1 wk of WR (82 and 61%, and these increases did not expand substantially after 2 (71 and 58%) and 3 wk (96 and 70%) of WR. This enhancement of hormone-stimulated 2-DG uptake in WR muscles preceded any alteration in glucose transporter (GLUT-4) protein level, which increased only after 2 (24%) and 3 wk (54%) of WR. Increases in GLUT-4 protein were significantly correlated (r = 0.844) with increases in citrate synthase. These results indicate that exercise training can enhance both insulin-stimulated and IGF-I-stimulated muscle glucose transport activity and that these improvements can develop without an increase in GLUT-4 protein.
authors.affiliation: Department of Physiology, University of Arizona College of Medicine, Tucson 85721-0093, USA.
authors.forename: J Y
authors.initials: JY
authors.lastname: Hokama
authors.forename: R S
authors.initials: RS
authors.lastname: Streeper
authors.forename: E J
authors.initials: EJ
authors.lastname: Henriksen
mesh_terms: D000818:Animals; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007334:Insulin-Like Growth Factor I; D005947:Glucose