title: Acute growth hormone administration causes exaggerated increases in plasma lactate and glycerol during moderate to high intensity bicycling in trained young men.
abstract: We studied the acute effects of a single, sc GH dose on exercise performance and metabolism during bicycling. Seven highly trained men [age, 26 +/- 1 yr (mean +/- SEM); weight, 77 +/- 3 kg; maximal oxygen uptake, 65 +/- 1 ml O(2).min(-1).kg(-1)] performed 90 min of bicycling 4 h after receiving 7.5 IU (2.5 mg) GH or placebo in a randomized, double-blinded, cross-over design trial. A standardized pre-exercise meal was given 2 h before exercise. Blood was sampled at rest and during exercise and analyzed for GH, IGF-I, glucose, lactate, insulin, glycerol, and nonesterified fatty acids (NEFA). In the placebo trial, all subjects completed the exercise protocol without any difficulties. In contrast, two subjects were not able to complete the exercise protocol in the GH trial, and one subject barely managed to complete the protocol. In addition, GH administration resulted in exaggerated increases in plasma lactate concentrations during exercise (P < 0.0001). The combined lipolytic effect of GH and exercise, evidenced by increased plasma glycerol and serum NEFA concentrations, was 3-fold greater than the effect of exercise alone (P < 0.0001), but this increased substrate availability did not result in increased whole body fat oxidation (indirect calorimetry). Plasma glucose was, on average, 9% higher during exercise after GH administration compared with placebo (P < 0.0001). We conclude that a single, relevant GH dose causes exaggerated increases in plasma lactate and glycerol as well as serum NEFA during 90 min of subsequent bicycling at moderate to high intensity. The exaggerated increase in plasma lactate may be associated with substantially decreased exercise performance.
authors.affiliation: Sports Medicine Research Unit, Building 8, Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark. klange@dadlnet.dk
authors.forename: Kai Henrik Wiborg
authors.initials: KH
authors.lastname: Lange
authors.forename: Benny
authors.initials: B
authors.lastname: Larsson
authors.forename: Allan
authors.initials: A
authors.lastname: Flyvbjerg
authors.forename: Rolf
authors.initials: R
authors.lastname: Dall
authors.forename: Morten
authors.initials: M
authors.lastname: Bennekou
authors.forename: Michael Højby
authors.initials: MH
authors.lastname: Rasmussen
authors.forename: Hans
authors.initials: H
authors.lastname: Ørskov
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D000328:Adult; D001642:Bicycling; D001786:Blood Glucose / Q000032:analysis; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005990:Glycerol / Q000097:blood*; D006339:Heart Rate; D006400:Hematocrit; D019382:Human Growth Hormone / Q000008:administration & dosage* / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D010101:Oxygen Consumption; D010807:Physical Endurance; D010919:Placebos
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D010919:Placebos; D019382:Human Growth Hormone; D019344:Lactic Acid; D007334:Insulin-Like Growth Factor I; D005990:Glycerol