Presence and activity of compounds with gnrh-like activity in the
ovary of seabream, sparus aurata.
Nabissi, Massimo, Debananda Pati, Alberta. M. Polzonetti-Magni, and
Hamid R. Habibi.
Department of Biology M.C.A., University of Camerino, via Camerini
2, 62032 Camerino (MC), Italy, and 2Department of Biological
Sciences, University of Calgary, Calgary, Alberta, Canada, T2N
1N4
APStracts 3:0238R, 1996.
The binding and activity of gonadotropin-releasing hormone (GnRH) was
characterized in the mature gilthead seabream (Sparus aurata) ovary,
using an analog of salmon GnRH ([ D-Arg6, Trp7, Leu8, Pro9- NEt];
sGnRH-A) as labeled ligand. The binding of 125I-sGnRH-A to seabream
ovarian membrane preparation was found to be saturable, displaceable,
reversible, and dependent on time, temperature and tissue
concentration. Addition of unlabeled s-GnRH-A displaced the
radioligand in a dose-related manner, indicating the presence of one
class of high affinity binding sites with a Kd value of 45.5 6.2 nM.
Addition of other GnRH peptides including salmon GnRH ([ Trp7, Leu8
]-GnRH; sGnRH) and chicken GnRH-II ([His5, Trp7, Tyr8]-GnRH; cGnRH)
also displaced 125I-sGnRH-A; all these peptides were found to bind
with lower affinities than that of sGnRH-A to the seabream ovarian
binding site. In this study, we also demonstrated the presence of
compounds with GnRH-like activity in the ovary of seabream. Seabream
ovarian extract was found to stimulate pituitary gonadotropin release
from the goldfish pituitary as well as displacing 125I-sGnRH-A
binding in the seabream ovary. Furthermore, addition of sGnRH-A to
cultured seabream oocytes was found to directly stimulate
reinitiation of oocyte meiosis as indicated by germinal vesicle
breakdown. Overall, the present study provides characterization of
GnRH binding sites in the seabream ovary, and supports the hypothesis
that GnRH or compounds with GnRH-like activity play an
autocrine/paracrine role in the regulation of ovarian function in the
seabream ovary.
Received 1 December 1995; accepted in final form 29 May 1996.
APS Manuscript Number R756-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96