AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 2 227-R234, Copyright © 1993 by American Physiological Society
Characterization of gonadotropin-releasing hormone receptors in goldfish ovary: variation during follicular development
D. Pati and H. R. Habibi
Department of Biological Sciences, University of Calgary, Alberta, Canada.
Gonadotropin-releasing hormone (GnRH) receptors were characterized in the
goldfish ovary using an analogue of salmon GnRH
([D-Arg6,Trp7,Leu8,Pro9-NEt]GnRH; sGn-RH-A) as a labeled ligand. Binding of
sGnRH-A to goldfish follicular membrane preparation was found to be
saturable, reversible, and dependent on time, temperature, tissue
concentration, and pH. Addition of unlabeled sGnRH-A displaced the bound
125I-labeled sGnRH-A in a dose-related manner. Hill plot as well as
Scatchard analysis indicated the presence of two classes of binding sites,
a high-affinity/low-capacity site and a low-affinity/high-capacity site, in
the fully mature and less mature goldfish ovary. However, immature goldfish
ovary contained only a single class of low-affinity binding sites. The
equilibrium association constants (Ka) of the low-affinity sites were found
to be similar in all follicular groups. However, there was a tendency for a
higher Ka value of the high-affinity sites in the less mature follicles
(0.5-0.95 mm) compared with the fully mature follicles (1.11-1.48 mm),
although the differences were not statistically significant. Bound
125I-sGnRH-A was also found to be displaceable by sGnRH ([Trp7,Leu8]GnRH)
and chicken GnRH-II (cGnRH-II; [His5,Trp7,Tyr8]GnRH), which occur naturally
in the goldfish brain. sGnRH-A and cGnRH-II were found to bind with greater
affinity than sGnRH to the goldfish ovarian GnRH binding sites.
