Endocrinology, Vol 105, 1369-1376, Copyright © 1979 by Endocrine Society

ARTICLES

Radioiodinated nondegradable gonadotropin-releasing hormone analogs: new probes for the investigation of pituitary gonadotropin-releasing hormone receptors

RN Clayton, RA Shakespear, JA Duncan, JC Marshall, PJ Munson and D Rodbard

Studies of pituitary plasma membrane gonadotropin-releasing hormone (GnRH) receptors using [125I]-iodo-GnRH suffer major disadvantages. Only a small (less than 25%) proportion of specific tracer binding is to high affinity sites, with more than 70% bound to low affinity sites (Ka = 1 x 10(6) M-1). [125I]Iodo-GnRH is also inactivated during incubation with pituitary plasma membrane preparations. Two superactive analongs of GnRH, substituted in positions 6 and 10, were used as the labeled ligand to overcome these problems. Both analogs bound to the same high affinity sites as GnRH on bovine pituitary plasma membranes, though the affinity of the analogs was higher than that of the natural decapeptide (Ka = 2.0 x 10(9), 6.0 x 10(9), and 3.0 x 10(8) M-1 for [D- Ser(TBu)6]des-Gly10-GnRH ethylamide, [D-Ala6]des-Gly10-GnRH ethylamide, and GnRH, respectively. The labeled analogs bound to a single class of high affinity sites with less than 15% of the specific binding being to low affinity sites (Ka approximately equal to 1 x 10(6) M-1). The labeled analogs were not inactivated during incubation with the pituitary membrane preparations. Using the analogs as tracer, a single class of high affinity sites (K1 = 4.0 x 10(9) M-1) was also demonstrated on crude 10,800 x g rat pituitary membrane preparations. Use of these analogs as both the labeled and unlabeled ligand offers substantial advantages over GnRH for investigation of GnRH receptors, allowing accurate determination of changes in their numbers and affinities under various physiological conditions.

This article has been cited by other articles:

				N. Eicke, A. R Gunthert, V. Viereck, D. Siebold, M. Behe, T. Becker, G. Emons, and C. Grundker GnRH-II receptor-like antigenicity in human placenta and in cancers of the human reproductive organs Eur. J. Endocrinol., October 1, 2005; 153(4): 605 - 612. [Abstract] [Full Text] [PDF]

				S. Chauvin, A. Bérault, Y. Lerrant, M. Hibert, and R. Counis Functional Importance of Transmembrane Helix 6 Trp279 and Exoloop 3 Val299 of Rat Gonadotropin-Releasing Hormone Receptor Mol. Pharmacol., March 1, 2000; 57(3): 625 - 633. [Abstract] [Full Text]

				C. A. Flanagan, B. J. Fromme, J. S. Davidson, and R. P. Millar A High Affinity Gonadotropin-Releasing Hormone (GnRH) Tracer, Radioiodinated at Position 6, Facilitates Analysis of Mutant GnRH Receptors Endocrinology, October 1, 1998; 139(10): 4115 - 4119. [Abstract] [Full Text] [PDF]

				J. D. Neill, L. W. Duck, L. C. Musgrove, and J. C. Sellers Potential Regulatory Roles for G Protein-Coupled Receptor Kinases and {beta}-Arrestins in Gonadotropin-Releasing Hormone Receptor Signaling Endocrinology, April 1, 1998; 139(4): 1781 - 1788. [Abstract] [Full Text] [PDF]

				E Loumaye, J Thorner, and K. Catt Yeast mating pheromone activates mammalian gonadotrophs: evolutionary conservation of a reproductive hormone? Science, December 24, 1982; 218(4579): 1323 - 1325. [Abstract] [PDF]

				E Loumaye and K. Catt Homologous regulation of gonadotropin-releasing hormone receptors in cultured pituitary cells Science, February 19, 1982; 215(4535): 983 - 985. [Abstract] [PDF]

				R. Savoy-Moore, N. Schwartz, J. Duncan, and J. Marshall Pituitary gonadotropin-releasing hormone receptors during the rat estrous cycle Science, August 22, 1980; 209(4459): 942 - 944. [Abstract] [PDF]