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

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 x 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.