EFFECTS ON GROWTH HORMONE SECRETION FOLLOWING INTRAVENOUS AND SUBCUTANEOUS INJECTIONS OF GROWTH HORMONE‐RELEASING FACTOR (hGRF‐44 NH2): COMPARISON OF IMMUNOREACTIVE PLASMA GRF LEVELS

Abstract

The effects of subcutaneous administration of three doses of human growth hormone-releasing factor (hGRF-44 NH₂ or hGRF) at doses of 100, 300 and 600 μg were studied in six normal young men. GH responses obtained with 100 and 300 μg were negligible. In contrast, the 600 μg dose gave a profile of response comparable in timing and magnitude to that obtained with i.v. hGRF at maximal effect doses (20, 80, 100 μg). Plasma immunoreactive hGRF levels (IR-hGRF) were compared after s.c. and i.v. hGRF. Mean maximal plasma concentrations were comparable with s.c. 600 μg and i.v. 20 μg. Peaks occurred earlier with i.v. hGRF (5 min as opposed to 15 min): however, return to undetectable values was obtained between 90 and 120 min after s.c. or i.v. injections. These data suggest a great loss of the peptide between the subcutaneous space and blood, without delayed absorption. High variability in plasma IR-hGRF concentrations between the subjects after the same s.c. doses was observed.