Stimulation of growth hormone secretion with human growth hormone releasing factors (GRF1-44, GRF1-40, GRF1-29) in normal subjects

Peptides of different chain lengths (GRF^1-44, GRF^1-40, GRF^1-29) were given as a 50 μg i.v. bolus to five normal volunteers. Blood was collected before and until 120 min after GRF injection. No serious side effects were recorded. All GRF peptides led to a clearcut and significant increase of GH levels compared to placebo controls with the maximum occurring 15-30 min after GRF injection. There was no significant difference in the maximal GH increase after the different GRF peptides. When GRF^1-44 was administered to five normal subjects over 2 days in 6- and 18-h intervals, respectively, significant increase of GH levels were recorded after each injection compared to placebo controls. Again, there was no significant difference between the maximal GH rises during the different tests. These findings show that the short GRF^1-29 peptide may be used for diagnosis and therapy. In addition, in contrast to continuous infusion and administration of GRF in short intervals, GRF application in 6-h intervals leads to adequate GH responses.