Endocrinology, Vol 101, 1850-1861, Copyright © 1977 by Endocrine Society

ARTICLES

Properties of the cytoplasmic progestin-binding protein in the rabbit uterus

D Philibert, T Ojasoo and J Raynaud

An exchange assay for the measurement of total cytoplasmic progestin binding sites has been developed on rabbit uterine cytosol using the highly potent progestin, R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene- 3,20-dione) labelled to a high specific activity. This compound has several advantages over progesterone: it is not bound by plasma corticosteroid binding globulin; it has high affinity for the progestin receptor; it binds virtually as fast as progesterone to the receptor, but the complex formed dissociated 8 times slower; its binding is not displaced by more than 2% by compounds devoid of progestational activity (estrogens, testosterone, dexamethasone, aldosterone). Bound endogenous progesterone was exchanged by tritiated R 5020 in a time compatible with receptor stability. At 0 C, total exchange of filled sites occurred in less than 4 h; at this temperature the R 5020- receptor complex was stable for at least 28 h. The conformation of the R 5020-receptor complex was investigated in sucrose density gradients under various experimental conditions. Unlike progesterone, it was possible to detect a 7S peak in uterine cytosol obtained from rabbits injected with a tracer dose of [3H]R 5020 1 h prior to sacrifice.

This article has been cited by other articles:

				P. Ferrari, L. Torielli, M. Ferrandi, G. Padoani, L. Duzzi, M. Florio, F. Conti, P. Melloni, L. Vesci, N. Corsico, et al. PST2238: A New Antihypertensive Compound That Antagonizes the Long-Term Pressor Effect of Ouabain J. Pharmacol. Exp. Ther., April 1, 1998; 285(1): 83 - 94. [Abstract] [Full Text]