Synthetic human growth hormone releasing factor (h-GRF-I-44-NH2) dose response effect on growth hormone and prolactin secretion in healthy adult men.

The dose-effect relationship of an i.v. bolus of synthetic h-GRF-44 on growth-hormone and prolactin secretion has been studied. Seven healthy adult volunteers received in a random order h-GRF-44 2.5, 5, 10, 20, 40 and 80 micrograms and a placebo. Plasma growth hormone (GH) was determined between 30 min before and 240 min after injection, the area under the curve (AUC) and the peak GH level being used to assess the response. For both parameters a dose-effect relationship was observed. Doses as low as 2.5 micrograms were capable of eliciting a rise in GH plasma levels in few patients. Above 40 micrograms the dose-effect curves tended to plateau, although the decrease in the slope of the dose-effect curve at the peak was more marked. Intersubject variability was large, so precise determination of the minimal effective dose as well as the lowest dose giving a maximal effect was not possible. The available evidence suggests that the i.v. dose of synthetic h-GRF-44 (SR 95228) which is likely to promote GH release into the blood stream in most healthy adults is within the range 40-100 micrograms. In these healthy adults unwanted effects were infrequent with these low doses. Unlike previous experience with higher doses of another synthetic h-GRF-44, prolactin secretion in this study was not affected.