title: Interactions of catecholestrogens with cytoplasmic and nuclear estrogen receptors in rat pituitary gland and hypothalamus.
abstract: The affinity of a series of catecholestrogens for 7S cytoplasmic receptor proteins from hypothalamus and pituitary gland of ovariectomised rats was assessed in vitro by a competitive charcoal binding assay at 4 degrees C. The equilibrium dissociation constants (Ki) of catecholestrogens 4-hydroxyestradiol, 4-hydroxyethynylestradiol, 2-hydroxyestradiol, 2-hydroxyethynylestradiol, and 4-hydroxyestrone were of the same order (Ki: 0.3-0.6 nM) as those of estradiol and ethnylestradiol (Ki: 0.1 nM). Methylation of 2-hydroxyestradiol led to a substantial loss of binding affinity. Tritium-labelled receptor complexes were demonstrated in KCl extracts of purified nuclei from pituitary and hypothalamic tissue 1 h after intravenous injection of 0.1 mCi tritiated 2- or 4-hydroxyestradiol. These macromolecular complexes sedimented in the 5-6S region of 5-20% (w/v) sucrose gradients containing 0.4 M-KCl. Further evidence for the translocation of estrogen receptors by catecholestrogens into the nuclei of rat pituitary and hypothalamus was the increase in nuclear receptor concentrations, measured by exchange assay, 1 h after the intraperitoneal injection of 0.1 mg unlabelled catecholestrogen. Administration of 4-hydroxyestradiol and 4-hydroxyethynylestradiol increased nuclear receptor concentrations to the same maximal levels as those following application of the same dose of estradiol or ethynylestradiol, whereas the respective 2-hydroxylated compounds exhibited only 60-70% of the maximal translocating capacity. The in vivo translocating capacities of the various catecholestrogens tested at this dose correlated well with their binding affinities for cytosol receptors determined in vitro.
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D004967:Estrogens / Q000494:pharmacology; D002393:Estrogens, Catechol / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D007031:Hypothalamus / Q000378:metabolism*; D007700:Kinetics; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011960:Receptors, Estrogen / Q000187:drug effects / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D004967:Estrogens; D002393:Estrogens, Catechol; D011960:Receptors, Estrogen; D004958:Estradiol