title: Preliminary characterization of an endogenous inhibitor of [3H]estradiol binding in rat uterine nuclei.
abstract: The rat uterus contains two classes of specific nuclear estrogen-binding sites which may be involved in estrogen action. Type I sites represent the classical estrogen receptor (Kd = 1 nM) and type II sites (Kd = 10-20 nM) are stimulated in the nucleus by estrogen under conditions which cause uterine hyperplasia. Dilution of uterine nuclear fractions from estrogen treated rats prior to quantitation of estrogen binding sites by [3H]estradiol exchange results in an increase (3- to 4-fold) in the measurable quantities of the type II site. Estimates of type I sites are not affected by dilution. These increases in type II sites following nuclear dilution occur independently of protein concentration and result from the dilution of a specific endogeneous inhibitor of [3H]estradiol binding to these sites. The inhibitor activity is present in cytosol preparations from rat uterus, spleen, diaphragm, skeletal muscle, and serum. Preliminary characterization of the inhibitor activity by Sephadex G-25 chromatography shows two distinct peaks which are similar in molecular weight (300). These components (alpha and beta) can be separated on LH-20 chromatography since the beta-peak component is preferentially retained on this lipophilic resin. Partial purification of the LH-20 beta inhibitor component by high performance liquid chromatography and gas-liquid chromatography-mass spectrometric analysis suggests the putative inhibitor activity is not steroidal in nature and consists of two very similar phenanthrene-like molecules (molecular weights 302 and 304). Analysis of cytosol preparations on LH-20 chromatography shows that non-neoplastic tissues (uterus, liver, lactating mammary gland) contain both and inhibitor components whereas estrogen-induced rat mammary tumors contain very low to nonmeasurable quantities of the beta-peak inhibitor activity.
mesh_terms: D000818:Animals; D002369:Castration; D002467:Cell Nucleus / Q000378:metabolism* / Q000502:physiology; D003600:Cytosol / Q000502:physiology; D004958:Estradiol / Q000378:metabolism*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D007700:Kinetics; D008970:Molecular Weight; D051381:Rats; D011959:Receptors, Estradiol; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014599:Uterus / Q000378:metabolism*
chemical_list: D011959:Receptors, Estradiol; D011960:Receptors, Estrogen; D004958:Estradiol