The effect of gonadotropin-releasing hormone on growth hormone and gonadotropin subunit gene expression in the pituitary of goldfish, Carassius auratus

The goldfish brain contains at least two forms of gonadotropin-releasing ho rmone (GnRH): sGnRH and cGnRH-II. In goldfish sGnRH and cGnRH-II are presen t both in the brain and pituitary, and exert direct effects via specific Gn RH receptors stimulating growth hormone (GH) and gonadotropin hormone (GtH) synthesis and secretion. In this study, we investigated the effects of sGn RH and cGnRH-II on GM subunit (alpha, FSH-beta and LH-beta) and GH mRNA lev els in the goldfish pituitary in vivo and in vitro. Injection of goldfish w ith sGnRH or cGnRH-II (4 mug/fish) stimulated GtH-alpha, FSH-beta and LH-be ta mRNA levels after 24 h. For in vitro studies, goldfish pituitary fragmen ts were treated continuously for 12 h with 10(-7) M sGnRH or cGnRH-II. Both sGnRH and cGnRH-II stimulated GtH-alpha, FSH-beta, LH-beta and GH mRNA lev els, however, cGnRH-II appeared to have a more pronounced effect. Similar e xperiments were carried out using cultured dispersed goldfish pituitary cel ls. In this study, treatments for 12 h with 10(-7) M sGnRH or cGnRH-II also stimulated GtH and GH gene expression. The present results provide a basis for the investigation of the signal transduction pathways that mediate GnR H-induced changes in GtH subunit and GH mRNA levels in the goldfish pituita ry. (C) 2001 Elsevier Science Inc. All rights reserved.