Characterization of gonadotropin-releasing hormone (GnRH) receptors in the ovary of common carp (Cyprinus carpio).
Gonadotropin-releasing hormone (GnRH) binding sites have been characterized in the fully mature common carp ovary, using an analog of salmon GnRH ([D-Arg6,Trp7,Leu8,Pro9-NEt]-GnRH; sGnRH-A) as a labeled ligand. Binding of sGnRH-A to carp follicular membrane preparation was found to be time-, temperature-, and pH-dependent. Optimal binding was achieved after 40 min of incubation at 4 degrees C at pH 7.6; binding was found to be unstable at room temperature. Binding of radioligand was a function of tissue concentration, with a linear correlation over the range of 8.0-40.0 micrograms membrane protein per tube. Incubation of membrane preparations with increasing levels of [125I]sGnRH-A revealed saturable binding at radioligand concentrations greater than 400 nM. The binding of [125I]sGnRH-A to the carp ovary was also found to be reversible; addition of unlabeled sGnRH-A (10(-6) M) after reaching equilibrium resulted in complete dissociation of [125I]sGnRH-A within 30 min, and the log dissociation plot indicated the existence of a single class of binding sites. Addition of unlabeled sGnRH-A displaced the bound [125I]sGnRH-A in a dose-related manner. Hill plot as well as Scatchard analysis suggested the presence of one class of high affinity GnRH binding sites. Bound [125I]sGnRH-A was also found to be displaceable by other GnRH peptides, including sGnRH ([Trp7,Leu8]-GnRH), cGnRH-II ([His5,Trp7,Tyr8]-GnRH) and a GnRH antagonist ([D-pGlu1,D-Phe2,D-PTrp3,6]-GnRH; GnRH-ANT) in a parallel fashion, indicating that these peptides bind to the same class of binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)
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Department of Biological Sciences, University of Calgary, Alta., Canada.
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D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002347:Carps / Q000378:metabolism*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D006080:Ovarian Follicle / Q000378:metabolism; D010053:Ovary / Q000378:metabolism*; D011966:Receptors, LHRH / Q000187:drug effects / Q000378:metabolism*; D013816:Thermodynamics
D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone