title: Regulation of glucose kinetics during intense exercise in humans: effects of alpha- and beta-adrenergic blockade.
abstract: This study examined the effect of combined alpha- and beta-adrenergic blockade on glucose kinetics during intense exercise. Six endurance-trained men exercised for 20 minutes at approximately 78% of their peak oxygen consumption (Vo(2)) following ingestion of a placebo (CON) or combined alpha- (prazosin hydrochloride) and beta- (timolol maleate) adrenoceptor antagonists (BLK). Plasma glucose increased during exercise in CON (0 minutes: 5.5 +/- 0.1; 20 minutes: 6.5 +/- 0.3 mmol. L(-1), P <.05). In BLK, the exercise-induced increase in plasma glucose was abolished (0 minutes: 5.7 +/- 0.3; 20 minutes: 5.7 +/- 0.1 mmol. L(-1)). Glucose kinetics were measured using a primed, continuous infusion of [6,6-(2)H] glucose. Glucose production was not different between trials; on average these values were 25.3 +/- 3.9 and 30.9 +/- 4.4 micromol. kg(-1). min(-1) in CON and BLK, respectively. Glucose uptake during exercise was greater (P <.05) in BLK (30.6 +/- 4.6 micromol. kg(-1). min(-1)) compared with CON (18.4 +/- 2.5 micromol. kg(-1). min(-1)). In BLK, plasma insulin and catecholamines were higher (P <.05), while plasma glucagon was unchanged from CON. Free fatty acids (FFA) and glycerol were lower (P <.05) in BLK. These findings demonstrate that adrenergic blockade during intense exercise results in a blunted plasma glucose response that is due to enhanced glucose uptake, with no significant change in glucose production.
authors.affiliation: Exercise, Muscle and Metabolism Unit, School of Health Sciences, Deakin University, Burwood, Australia.
authors.forename: Kirsten F
authors.initials: KF
authors.lastname: Howlett
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Watt
authors.forename: Mark
authors.initials: M
authors.lastname: Hargreaves
authors.forename: Mark A
authors.initials: MA
authors.lastname: Febbraio
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006439:Hemodynamics / Q000502:physiology; D006728:Hormones / Q000097:blood; D006801:Humans; D007700:Kinetics; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D011224:Prazosin / Q000494:pharmacology; D015656:Respiratory Mechanics / Q000502:physiology; D013999:Timolol / Q000494:pharmacology
chemical_list: D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D006728:Hormones; D019344:Lactic Acid; D013999:Timolol; D005947:Glucose; D009638:Norepinephrine; D011224:Prazosin; D004837:Epinephrine