title: Time course of insulin sensitivity and skeletal muscle glycogen synthase activity after a single bout of exercise in horses.
abstract: The time course of insulin sensitivity, skeletal muscle glycogen and GLUT4 content, and glycogen synthase (GS) activity after a single bout of intense exercise was examined in eight horses. On separate days, a euglycemic-hyperinsulinemic clamp (EHC) was undertaken at 0.5, 4, or 24 h after exercise or after 48 h of rest [control (Con)]. There was no increase in mean glucose infusion rate (GIR) with exercise (0.5-, 4-, and 24-h trials), and GIR was significantly decreased at 0.5 h postexercise (GIR: 8.6 +/- 2.7, 6.7 +/- 2.0, 9.0 +/- 2.0, and 10.6 +/- 2.2 mg.kg(-1).min(-1) for Con and at 0.5, 4, and 24 h, respectively). Before each EHC, muscle glycogen content (mmol glucosyl units/kg dry muscle) was higher (P < 0.05) for Con (565 +/- 102) than for other treatments (317 +/- 84, 362 +/- 79, and 382 +/- 74 for 0.5, 4, and 24 h, respectively) and muscle GLUT4 content was unchanged. Pre-EHC active-to-total GS activity ratio was higher (P < 0.05) at 0.5, 4, and 24 h after exercise than in Con. Post-EHC active GS and GS activity ratio were higher (P < 0.05) in Con and at 24 h. There was a significant inverse correlation (r = -0.43, P = 0.02) between glycogen content and GS activity ratio but no relationship between GS activity and GIR. The lack of increase in insulin sensitivity, determined by EHC, after exercise that resulted in a significant reduction in muscle glycogen content is consistent with the slow rate of muscle glycogen resynthesis observed in equine studies.
authors.affiliation: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Shannon E
authors.initials: SE
authors.lastname: Pratt
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Geor
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Spriet
authors.forename: L Jill
authors.initials: LJ
authors.lastname: McCutcheon
mesh_terms: D000818:Animals; D005260:Female; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000502:physiology*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D006003:Glycogen; D006006:Glycogen Synthase