Hexarelin-induced growth hormone, cortisol, and prolactin release: A dose-response study

Dose-response data for GH-releasing peptides are limited. We studied the effects of varying doses (0-1.0 mu g/kg) of hexarelin, a novel GH-releasing peptide, administered iv to healthy adult males on GH, PRL, and cortisol release. In addition, we studied the effect of administration of a single dose of GHRH-(1-29)-NH2 (1.0 mu g/kg), alone or in combination with a low dose of hexarelin (0.125 mu g/kg). Dose-response curves for the maximum GH response and maximum percent change in serum PRL and cortisol concentrations from baseline were constructed. The GH dose-response curve reached a plateau of 140 mU/L, corresponding to a hexarelin dose of 1.0 mu g/kg, with an ED(50) of 0.48+/-0.02 mu g/kg (mean+/-SEM). The PRL dose-response curve reached a plateau of 180% for the maximum percent rise from baseline, corresponding to a hexarelin dose of 1.0 mu g/kg, with an ED(50) of 0.39+/-0.02 mu g/kg. The cortisol dose-response curve showed a step increase to approximately 40% at a hexarelin dose of 0.5 mu g/kg. The coadministration of GHRH-(1-29-NH2 (1.0 mu g/kg) and low dose hexarelin 10.125 mu g/kg) resulted in massive GH release (115+/-32.8 mU/L), a moderate rise in serum PBL (84.9+/-27.5%), and no rise in serum cortisol. These data show that iv hexarelin was capable of inducing GH, PRL, and cortisol release in a dose-dependent manner. Low dose hexarelin was synergistic with GHRH and potent for GH release with a minimal effect on other hormones.