title: Role of insulin on exercise-induced GLUT-4 protein expression and glycogen supercompensation in rat skeletal muscle.
abstract: The purpose of this study was to investigate the role of insulin on skeletal muscle GLUT-4 protein expression and glycogen storage after postexercise carbohydrate supplementation. Male Sprague-Dawley rats were randomly assigned to one of six treatment groups: sedentary control (Con), Con with streptozocin (Stz/C), immediately postexercise (Ex0), Ex0 with Stz (Stz/Ex0), 5-h postexercise (Ex5), and Ex5 with Stz (Stz/Ex5). Rats were exercised by swimming (2 bouts of 3 h) and carbohydrate supplemented immediately after each exercise session by glucose intubation (1 ml of a 50% wt/vol). Stz was administered 72-h before exercise, which resulted in hyperglycemia and elimination of the insulin response to the carbohydrate supplement. GLUT-4 protein of Ex0 rats was 30% above Con in fast-twitch (FT) red and 21% above Con in FT white muscle. In Ex5, GLUT-4 protein was 52% above Con in FT red and 47% above Con in FT white muscle. Muscle glycogen in FT red and white muscle was also increased above Con in Ex5 rats. Neither GLUT-4 protein nor muscle glycogen was increased above Con in Stz/Ex0 or Stz/Ex5 rats. GLUT-4 mRNA in FT red muscle of Ex0 rats was 61% above Con but only 33% above Con in Ex5 rats. GLUT-4 mRNA in FT red muscle of Stz/C and Stz/Ex0 rats was similar but significantly elevated in Ex5/Stz rats. These results suggest that insulin is essential for the increase in GLUT-4 protein expression following postexercise carbohydrate supplementation.
authors.affiliation: Department of Kinesiology and Health Education, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Chia-Hua
authors.initials: CH
authors.lastname: Kuo
authors.forename: Hyonson
authors.initials: H
authors.lastname: Hwang
authors.forename: Man-Cheong
authors.initials: MC
authors.lastname: Lee
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Castle
authors.forename: John L
authors.initials: JL
authors.lastname: Ivy
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D015870:Gene Expression; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000378:metabolism*; D006943:Hyperglycemia / Q000378:metabolism / Q000503:physiopathology; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000235:genetics*; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013311:Streptozocin / Q000494:pharmacology
chemical_list: D000903:Antibiotics, Antineoplastic; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat; D013311:Streptozocin; D006003:Glycogen