Synergy of L-arginine and GHRP-2 stimulation of growth hormone in men and women: modulation by exercise.
We investigated the ability of exercise, a multipathway, potent, physiological stimulus for GH release, to alter the synergistic interaction of L-arginine (A) and GH-related peptide (GHRP)-2 (G) observed at rest and the ability of gender to further modulate this putative interaction. Subjects (9 men and 9 early follicular phase women) completed 30 min of constant load aerobic exercise in combination with intravenous infusions of saline (S), A (30 g over 30 min), G (1 microg/kg bolus), or both (AG) in separate study sessions in randomly assigned order. Measures of GH release were logarithmically transformed for statistical analysis. Similar to rest, exercise maintained the rank order (AG > G > A > S) of effective stimulation of GH release for the key response measures in men or women, a gender disparity in the time to reach the maximal serum GH concentration, the calculated endogenous GH half-life, and the observed effect of preinfusion (basal) serum GH concentrations on determining secretagogue responsiveness. Exercise potentiated the individual stimulatory actions of A and G, while blunting the relative magnitude of the synergistic (supra-additive) interaction observed at rest. We infer from the present data that 1) exercise is likely to induce release of both GHRH and somatostatin, 2) L-arginine may facilitate the effect of exercise by limiting somatostatin release, 3) GHRP-2 could further enhance the stimulatory impact of exercise by opposing central actions of somatostatin and/or heightening endogenous GHRH release, and 4) gender strongly controls the relative but not absolute magnitude of A/G synergy both at rest and after exercise.
Wideman
L
L
Department of Internal Medicine, University of Virginia, Charlottesville, Virginia 22903, USA.
Weltman
J Y
JY
Patrie
J T
JT
Bowers
C Y
CY
Shah
N
N
Story
S
S
Veldhuis
J D
JD
Weltman
A
A
D000328:Adult; D000704:Analysis of Variance; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology*; D004357:Drug Synergism; D004734:Energy Metabolism / Q000187:drug effects; D015444:Exercise / Q000502:physiology*; D005260:Female; D005498:Follicular Phase; D006728:Hormones / Q000008:administration & dosage / Q000494:pharmacology*; D019382:Human Growth Hormone / Q000097:blood / Q000378:metabolism*; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects; D005082:Physical Exertion / Q000502:physiology*; D012044:Regression Analysis; D012727:Sex Characteristics
D006728:Hormones; D009842:Oligopeptides; D019382:Human Growth Hormone; D001120:Arginine; C091874:growth hormone-releasing peptide-2