Effect of GHRP-6 and GHRH on GH secretion in rats following chronic glucocorticoid treatment.
The aim of our study was to investigate the effects of His-DTrp-Ala-Trp-Phe-Lys-NH2 (GHRP-6) on baseline and growth hormone-releasing hormone (GHRH) stimulated growth hormone (GH) release in conscious, freely-moving rats receiving chronic glucocorticoid treatment. Animals were treated daily for seven days with either vehicle or dexamethasone (dex, 40 micrograms/day). On the day of experimentation, rats received an i.v. injection of saline or GHRP-6 followed 15 min later by an i.v. injection of saline or rat GHRH. Three doses of GHRP-6 were evaluated, 1 microgram, 4 micrograms and 25 micrograms/kg; one dose of GHRH was evaluated, 500 ng/kg. GHRP-6 increased plasma GH levels over baseline concentrations in a dose-dependent fashion both in vehicle- and dex-treated rats. The GH response to GHRP-6 and GHRH was significantly less in dex-treated rats as compared to vehicle-treated rats. The combined administration of GHRP-6 and GHRH did not result in any change in plasma GH levels which could not be predicted from the administration of either peptide alone. Our results show that GHRP-6 is able to stimulate GH secretion in glucocorticoid-treated rats but it is unable to counteract the glucocorticoid-induced inhibition of GH secretion.
Voltz
D M
DM
Department of Health Sciences, University of Wisconsin-Milwaukee 53211.
Piering
A W
AW
Magestro
M
M
Giustina
A
A
Wehrenberg
W B
WB
D000595:Amino Acid Sequence; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology*; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D009842:Oligopeptides; C041048:growth hormone releasing hexapeptide; D003907:Dexamethasone; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone