Long-term effects of human growth hormone on plasma amino acids transport in hypopituitary dwarfism.

Abstract

ABSTRACT The chronic effects of human growth hormone (hGH) on the transport of plasma amino acids (PAA) induced by glucose administration were studied in 17 patients with GH deficiency at different stages in the course of GH therapy. The study comprised 9 patients before and after 2–3 months of the therapy and 8 patients after prolonged treatment of 2–3 years. Five normal children served as controls. Analysis of 13 neutral and acidic PAA concentrations before and 2 h after glucose loading was carried out, and a decrease in PAA was expressed as a percentage of 2 h value to the initial level (PAA ratio). Fasting levels of several PAA before treatment were significantly lower than those of controls which gradually rose during the course of the therapy. The mean ± sd value of PAA ratio was also reduced before treatment (68 ± 16 %) vs. that of controls (82 ± 16 %, P < 0.05), which rose after 2–3 months of GH therapy to a comparable level of controls (91 ± 26 %). In patients treated for 2–3 years, however, PAA ratio was decreased to the level of pre-treatment (57 ± 17 %), P < 0.01 vs. control). These changes were pronounced in glucogenic, branched-chain and aromatic amino acids. Serum gamma-glutamyltranspeptidase (GGTP) activity was also low before GH therapy and normalized by the treatment. However, no significant correlation was noted between PAA ratio and serum GGTP activity or GH level. These results indicate that PAA transport evoked by endogenous insulin changes considerably according to the duration of GH therapy, and this may reflect a peripheral alteration of responsiveness to exogenous GH in the prolonged course of GH therapy in pituitary dwarfs.