Characterization of gonadotropin-releasing hormone receptors in goldfish ovary: variation during follicular development.
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.
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Department of Biological Sciences, University of Calgary, Alberta, Canada.
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D000818:Animals; D001665:Binding Sites; D005260:Female; D006054:Goldfish / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D006080:Ovarian Follicle / Q000502:physiology*; D010053:Ovary / Q000378:metabolism*; D011966:Receptors, LHRH / Q000378:metabolism*; D012474:Salmon
D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone