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Biology of Reproduction, Vol 51, 349-357, Copyright © 1994 by Society for the Study of Reproduction

ARTICLES

Receptor binding of gonadotropin-releasing hormone antagonists that inhibit release of gonadotropin-II and growth hormone in goldfish, Carassius auratus

CK Murthy, AO Wong, HR Habibi, JE Rivier and RE Peter
Department of Zoology, University of Alberta, Edmonton, Canada.

In goldfish, GnRH stimulates gonadotropin-II (GTH-II) and growth hormone (GH) release. The two native forms of GnRH, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), bind to two classes of GnRH binding sites: high-affinity/low-capacity sites and low-affinity/high-capacity sites. Our previous in vitro perifusion studies of goldfish pituitary fragments showed that [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E), [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-sGnRH (analog C), and [Ac-D(2)Nal1, 4Cl-D-Phe2, D-(3)Pal3,6]-cGnRH-II (analog N) inhibited both sGnRH- and cGnRH-II-stimulated GTH-II and GH release. Interestingly, analog C stimulated GH release but not GTH-II release. The objectives of the present study were 1) to test the site of action of GnRH antagonists in goldfish, 2) to test the relationship between receptor binding affinity of antagonists and their in vitro inhibitory potencies and apparent duration of action, and 3) to compare the binding characteristics of analog C with its differential action on GTH- II and GH release. As in previous studies, analog E suppressed sGnRH- stimulated GTH-II and GH release from perifused pituitary fragments. Similarly, analog E suppressed both sGnRH- and cGnRH-II-stimulated GTH- II and GH release from perifused dispersed goldfish pituitary cells, indicating the direct action of GnRH antagonists at the pituitary cell level. In the receptor binding studies, analog E displaced 125I-[D- Arg6, Pro9NHEt]-sGnRH (sGnRH-A) from crude goldfish pituitary membrane preparations in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)


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C. A. Flanagan, C.-C. Chen, M. Coetsee, S. Mamputha, K. E. Whitlock, N. Bredenkamp, L. Grosenick, R. D. Fernald, and N. Illing
Expression, Structure, Function, and Evolution of Gonadotropin-Releasing Hormone (GnRH) Receptors GnRH-R1SHS and GnRH-R2PEY in the Teleost, Astatotilapia burtoni
Endocrinology, October 1, 2007; 148(10): 5060 - 5071.
[Abstract] [Full Text] [PDF]


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Copyright © 1994 by the Society for the Study of Reproduction.