Interactions of Catecholestrogens with Cytoplasmic and Nuclear Estrogen Receptors in Rat Pituitary Gland and Hypothalamus |
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Authors: | Josef Kirchhoff Elisabeth Hornung Rüdiger Ghraf Peter Ball Rudolf Knuppen |
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Institution: | Institut für Physiologische Chemie, Universitätsklinikum Essen, Essen;and;Institut für Biochemische Endokrinologie, Medizinische Hochschule Lübeck, Lübeck, Federal Republic of Germany |
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Abstract: | 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°C. The equilibrium dissociation constants ( K i) of catecholestrogens 4-hydroxyestradiol, 4-hydroxyethynylestradiol, 2-hydroxyestradiol, 2-hydroxyethynylestradiol, and 4-hydroxyestrone were of the same order ( K i 0.3–0.6 n m ) as those of estradiol and ethynylestradiol ( K i: 0.1 n m ). 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. |
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Keywords: | Estrogen receptors Pituitary gland Hypothalamus 2-Hydroxyestro-gens 4-Hydroxyestrogens |
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