Growth hormone (GH)-releasing peptide-6 requires endogenous hypothalamic GH-releasing hormone for maximal GH stimulation.
GH-releasing peptide-6 (GHRP-6) is a potent GH secretagogue that releases GH by uncertain mechanisms. To assess whether GHRH is required for GH release by GHRP-6 in humans, we used the specific antagonist to GHRH (N-Ac-Tyr1,D-Arg2)GHRH(1-29)NH2 (GHRH Ant). We have previously shown that GHRH-Ant (400 microg/kg) blocked the GH response to 0.33 and 3.3 microg/kg boluses of GHRH by 95% and 81%, respectively. Nine healthy men between the ages of 20 and 30 yr were studied on two occasions. They received either saline or GHRH-Ant (400 microg/kg, i.v.) at 0840 h, followed by GHRP-6 (1 microg/kg, i.v. bolus) at 0900 h. Blood was sampled every 10 min from 0800-1100 h. GH responses were measured as the maximal increase over the baseline GH concentration and as the area under the curve. GHRH-Ant eliminated most of the GH response to GHRP-6 [maximal increase over the baseline GH concentration, 33.8 +/- 4.8 vs. 6.2 +/- 1.8 microg/L (mean +/- SEM; P < 0.0001); area under the curve, 1701 +/- 278 vs. 376 +/- 113 microg/min x L (P < 0.001)]. These data show that endogenous GHRH is necessary for most of the GH response to GHRP-6 in humans.
Pandya
N
N
Department of Internal Medicine, University of Michigan and Ann Arbor Veterans Affairs Medical Center, 48109-0354, USA.
DeMott-Friberg
R
R
Bowers
C Y
CY
Barkan
A L
AL
Jaffe
C A
CA
D000328:Adult; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D013007:Growth Hormone-Releasing Hormone / Q000502:physiology*; D006728:Hormones / Q000494:pharmacology*; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology*; D012636:Secretory Rate / Q000187:drug effects; D017337:Sermorelin / Q000031:analogs & derivatives / Q000494:pharmacology; D013268:Stimulation, Chemical
D006728:Hormones; D009842:Oligopeptides; D019382:Human Growth Hormone; D007987:Gonadotropin-Releasing Hormone; C041048:growth hormone releasing hexapeptide; D017337:Sermorelin; D013007:Growth Hormone-Releasing Hormone; C058677:somatotropin releasing hormone (1-29)amide, N-acetyl-tyrosyl(1)-arginyl(2)-