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Effects of High-Dose Growth Hormone on Glucose and Glycerol Metabolism at Rest and during Exercise in Endurance-Trained Athletes

Department of Diabetes and Endocrinology, Guy’s, King’s and St. Thomas’ School of Medicine, St. Thomas Hospital, London SE1 7EH, United Kingdom

Address all correspondence and requests for reprints to: Dr. James Gibney, Department of Endocrinology, Adelaide & Meath Hospitals, incorporating the National Children’s Hospital, Tallaght, Dublin 24, Ireland. E-mail: j.gibney{at}amnch.ie.

Context: Recombinant human-GH (r-hGH), in supraphysiological doses, is self-administered by athletes in the belief that it is performance enhancing.

Objective: The objective of this study was to determine whether r-hGH alters whole-body glucose and glycerol metabolism in endurance-trained athletes at rest and during and after exercise.

Design: This was a 4-wk double-blind placebo-controlled trial.

Setting: This study was conducted at St. Thomas Hospital (London, UK).

Participants: Twelve endurance-trained male athletes were recruited and randomized to r-hGH (0.2 U/kg·d) (n = 6) or identical placebo (n = 6) for 4 wk. One (placebo group) withdrew after randomization.

Intervention: Intervention was conducted by randomization to r-hGH (0.2 U/kg·d) or identical placebo for 4 wk.

Main Outcome Measures: Whole-body rates of appearance (Ra) of glucose and glycerol (an index of lipolysis) and rate of disappearance of glucose were measured using infusions of D-[6–6-²H₂]glucose and ²H₅-glycerol.

Results: Plasma levels of glycerol and free fatty acids and glycerol Ra at rest and during and after exercise increased during r-hGH treatment (P < 0.05 vs. placebo). Glucose Ra and glucose rate of disappearance were greater after exercise during r-hGH treatment (P < 0.05 vs. placebo). Resting energy expenditure and fat oxidation were greater under resting conditions during r-hGH treatment (P < 0.05 vs. placebo).

Conclusions: r-hGH in endurance-trained athletes increased lipolysis and fatty acid availability at rest and during and after exercise. r-hGH increased glucose production and uptake rates after exercise. The relevance of these effects for athletic performance is not known.

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