ACUTE GROWTH-HORMONE EFFECTS ON AMINO-ACID AND LIPID-METABOLISM

The anabolic actions of GH are well known, although specific tissue re sponses and the mechanism of nitrogen conservation are less well under stood, This study was designed to examine the acute metabolic effects of GH on whole body and regional protein metabolism, using an experime ntal protocol which controlled for confounding perturbations in other hormones by a simultaneous infusion of somatostatin. Control subjects received replacement doses of insulin, glucagon, and GH for the entire 7-h study period, whereas GH subjects received an identical protocol, except for an increased dose of GH sufficient to increase serum conce ntrations into the high-physiological range (12-20 ng/mL) for the fina l 3.5 h of the study (P < 0.001). Thirteen young, healthy male subject s were studied in the postabsorptive period; five served as control su bjects and eight as treatment (GH) subjects. Each received continuous iv infusions of somatostatin, L-[(13)-C]leucine, and L-[H-2(5)]phenyla lanine throughout the study. Femoral arterial and venous sampling allo wed for simultaneous measurements across the leg and in the whole body . C-Peptide levels were suppressed throughout the infusion; insulin, g lucagon, insulin-like growth factor I, cortisol, epinephrine, norepine phrine, and glucose concentrations were not different between groups. Glycerol concentrations increased 3-fold in GH subjects during the fin al 3.5-h period (P = 0.04). Concentrations of several amino acids decl ined through the study, but no differences were observed between treat ment groups. Leucine oxidation was reduced in GH compared to control s ubjects (P = 0.04). No changes in CO2 production or whole body leucine or phenylalanine flux were observed, whereas nonoxidative disposal of leucine was marginally higher in GH compared to control subjects (P = 0.07). By contrast, rates of appearance and disappearance of both leu cine and phenylalanine across the leg all were relatively lower in GH compared to control subjects; leucine balance across the leg was reduc ed by GH (P = 0.03), whereas phenylalanine balance was not influenced by GPI. Our data thus demonstrate an acute stimulatory effect of GH on lipolysis, a decrease in leucine oxidation, and no stimulation of mus cle protein synthesis in spite of enhanced protein synthesis in nonmus cle tissue.