Supplemental growth hormone alters body composition, muscle protein metabolism and serum lipids in fit adults: characterization of dose-dependent and response-recovery effects.

Using double-blind, placebo-controlled procedures, the effects of low and high therapeutic dosages of methionyl-human growth hormone (met-hGH) on body composition, muscle protein metabolism and serum lipids were studied in 7 fit adults without growth hormone (GH) deficiency. Dose-dependent changes in body composition were observed that in part appeared to be influenced by a response-recovery effect, as measured by responses factored according to the duration of washout between exposure to the low and high dosages of met-hGH (6 weeks vs. 12 weeks vs. 18 weeks). Increases in fat-free weight were accompanied by an increase in skeletal muscle protein metabolism. Basal levels of cholesterol were inversely related to peak levels of GH in response to exercise stimulation and IGF-I, while GH supplementation lowered levels of total cholesterol and high- and low-density lipoproteins. A dose-dependent effect occurred for total cholesterol, and the percent change in cholesterol was related to the percent change in insulin-like growth factor I (IGF-I). Endogenous levels of GH were attenuated in response to stimulation and IGF-I levels were increased after treatment with GH, but no dose-dependent changes were observed. We conclude that met-hGH alters body composition and muscle protein metabolism, and decreases stored and circulating lipids in fit adults with a pre-existing supranormal body composition. The physiological profile of the person was not as important as the treatment conditions in determining the somatic and physiological response outcomes.