Synergy of L-arginine and growth hormone (GH)-releasing peptide-2 on GH release: influence of gender

We test the hypotheses that 1) growth hormone (GH)-releasing peptide-2 (G) synergizes with L-arginine (A), a compound putatively achieving selective s omatostatin withdrawal and 2) gender modulates this synergy on GH secretion . To these ends, 18 young healthy volunteers (9 men and 9 early follicular phase women) each received separate morning intravenous infusions of saline (S) or A (30 g over 30 min) or G (1 mu g/kg) or both, in randomly assigned order. Blood was sampled at 10-min intervals for later chemiluminescence a ssay of serum GH concentrations. Analysis of covariance revealed that the p reinjection (basal) serum GH concentrations significantly determined secret agogue responsiveness and that sex (P = 0.02) and stimulus type (P < 0.001) determined the slope of this relationship. Nested ANOVA applied to log-tra nsformed measures of GH release showed that gender determines 1) basal rate s of GH secretion, 2) the magnitude of the GH secretory response to A, 3) t he rapidity of attaining the GH maximum, and 4) the magnitude or fold (but not absolute) elevation in GH secretion above preinjection basal, as driven by the combination of A and G. In contrast, the emergence of the G and A s ynergy is sex independent. We conclude that gender modulates key facets of basal and A/G-stimulated GH secretion in young adults.