Effects of gonadotropin-releasing hormone on growth hormone secretion and gene expression in common carp pituitary

Abstract

Using radioimmuno- and ribonuclease protection assays, we examined the effects of gonadotropin-releasing hormone and its analogs on the growth hormone mRNA level and growth hormone secretion in common carp (Cyprinus carpio) pituitary fragments with static incubation. After a 24 h treatment, sGnRH ([Trp7,Leu8]-LHRH) and sGnRH-A ([D-Arg6,Pro9]-LHRH) (0.1 nM-1 μM) elevated the GH mRNA level and stimulated the GH secretion in a dose-dependent manner, with a higher potency for sGnRH-A. In a time-course experiment, the function of sGnRH and sGnRH-A (10 nM) on GH secretion was observed after 6 h incubation, while no action on the GH mRNA level were noted until 12 h after treatment. Comparing mammalian GnRH, avian GnRH and piscine GnRH, sGnRH and sGnRH-A showed the highest potency in increasing GH mRNA level and GH-release, followed by cGnRH-II ([His5,Tyr8]-LHRH), and finally LHRH and LHRH-A([D-Trp6, Pro9]-LHRH). These findings, taken together, suggest that GnRH not only can influence GH release, but also play a role in the regulation of GH synthesis. © 2002 Elsevier Science Inc. All rights reserved.