Inhibition of the growth hormone (GH) response to GH-releasing hormone by constant Met-GH infusions

GH release is controlled by hypothalamic hormones and insulin-like growth factor I, synthesized under the influence of GH, and perhaps also by GH itself. The availability of recombinant Met-GH was the basis for studies aimed at 1) obtaining constant serum GH levels by means of constant Met-GH infusions (40 and 80 ng/kg.min for 6 h), and 2) evaluating the metabolic effects of constant GH levels and, in particular, their effects on the serum GH response to GHRH. In six normal men, both Met-GH infusions increased plasma FFA levels, but did not alter the circulating levels of somatostatin, insulin-like growth factor I, insulin, glucose, cholesterol, and triglycerides. The Met-GH infusions did cause a dose-related inhibition of GHRH-induced GH release. These data indicate that it is possible to maintain constant serum GH levels by means of constant Met-GH infusions at different infusion rates, and that GH inhibits its own release.