title: Glucose infusion attenuates endogenous glucose production and enhances glucose use of horses during exercise.
abstract: We examined the effects of increased glucose availability on glucose kinetics and substrate utilization in horses during exercise. Six conditioned horses ran on a treadmill for 90 min at 34 +/- 1% of maximum oxygen uptake. In one trial [glucose (Glu)], glucose was infused at a mean rate of 34.9 +/- 1.1 micromol. kg(-1). min(-1), whereas in the other trial [control (Con)] an equivalent volume of isotonic saline was infused. Plasma glucose increased during exercise in Glu (90 min: 8.3 +/- 1.7 mM) but was largely unchanged in Con (90 min: 5.1 +/- 0.4 mM). In Con, hepatic glucose production (HGP) increased during exercise, reaching a peak of 38.6 +/- 2.7 micromol. kg(-1). min(-1) after 90 min. Glucose infusion partially suppressed (P < 0.05) the rise in HGP (peak value 25.8 +/- 3.3 micromol. kg(-1). min(-1)). In Con, glucose rate of disappearance (R(d)) rose to a peak of 40.4 +/- 2.9 micromol. kg(-1). min(-1) after 90 min; in Glu, augmented glucose utilization was reflected by values for glucose R(d) that were twofold higher (P < 0.001) than in Con between 30 and 90 min. Total carbohydrate oxidation was higher (P < 0.05) in Glu (187.5 +/- 8.5 micromol. kg(-1). min(-1)) than in Con (159.2 +/- 7.3 micromol. kg(-1).min(-1)), but muscle glycogen utilization was similar between trials. We conclude that an increase in glucose availability in horses during low-intensity exercise 1) only partially suppresses HGP, 2) attenuates the decrease in carbohydrate oxidation during such exercise, but 3) does not affect muscle glycogen utilization.
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio 43210, USA. rgeor@ker.com
authors.forename: R J
authors.initials: RJ
authors.lastname: Geor
authors.forename: K W
authors.initials: KW
authors.lastname: Hinchcliff
authors.forename: R A
authors.initials: RA
authors.lastname: Sams
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D050260:Carbohydrate Metabolism; D004734:Energy Metabolism; D005260:Female; D005947:Glucose / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology*; D006003:Glycogen / Q000378:metabolism; D006728:Hormones / Q000097:blood; D006736:Horses / Q000378:metabolism / Q000502:physiology*; D007262:Infusions, Intravenous; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism; D009994:Osmolar Concentration; D010084:Oxidation-Reduction
chemical_list: D001786:Blood Glucose; D006728:Hormones; D006003:Glycogen; D005947:Glucose