title: Glucose kinetics during exercise in trained men.
abstract: Six trained men were studied to examine the relative increases in hepatic glucose output and peripheral glucose uptake during 40 min of exercise at 75% VO2max. Rates of appearance (Ra) and disappearance (Rd) were measured using a primed, continuous intravenous infusion of D-[3-3H]glucose. Plasma glucose increased (P < 0.05) from 4.8 +/- 0.2 mmol l-1 at rest to 6.2 +/- 0.5 mmol l-1 after 40 min of exercise. Both Ra and Rd increased (P < 0.05) during exercise, however, during the early phase of exercise, Ra exceeded Rd (P < 0.05). Ra peaked at 42.0 +/- 3.2 mumol kg-1 min-1 after approximately 15 min of exercise. In contrast, the highest Rd of 33.9 +/- 4.3 mumol kg-1 min-1 was measured at the end of exercise. In additional experiments, five men were studied during 40 min of exercise at 70-75% VO2max, 2 h after ingestion of the non-selective beta-adrenergic antagonist timolol or a placebo capsule. Subjects were unable to complete the exercise bout following timolol, fatiguing after 28.0 +/- 4.0 min (P < 0.05). The increase in blood glucose from 4.3 +/- 0.1 to 4.7 +/- 0.3 mmol l-1 (P < 0.05) following 20 min of exercise under control conditions was completely abolished by prior timolol ingestion (4.2 +/- 0.2 to 4.1 +/- 0.2 mmol l-1). These results demonstrate that during exercise at 75% VO2max in trained men, hepatic glucose output is not always closely matched to peripheral muscle glucose uptake and may be subject to feed-forward regulation.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, University of Melbourne, Parkville, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Hargreaves
authors.forename: J
authors.initials: J
authors.lastname: Proietto
mesh_terms: D000284:Administration, Oral; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D015444:Exercise / Q000502:physiology*; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics*; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D009132:Muscles / Q000378:metabolism; D010809:Physical Fitness / Q000502:physiology*; D013999:Timolol / Q000008:administration & dosage / Q000494:pharmacology; D014316:Tritium
chemical_list: D001786:Blood Glucose; D014316:Tritium; D013999:Timolol; D005947:Glucose