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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 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 (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 ethynylestradiol (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.
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The ability of Catecholestrogens to induce cytosolic progestin binding sites in the hypothalamus, pituitary gland and uterus of ovariectomised-adrenal-ectomised rats was demonstrated by the increase in high-affinity [3H]promegestone binding sites (KD 1.39,0.50 and 0.54 n M, respectively) following a single subcutaneous injection (26.4 μg/animal) of the 3, 4-dibenzoate ester of 4-hydroxyestradiol. The affinity and the time course of induction of these binding sites were very similar to those after a single injection of an equivalent dose (20 (μg/animal) of estradiol 3-benzoate, exhibiting maximal receptor levels after 44 h. Widely differing efficacies in the induction of progestin binding sites were observed between the dibenzoate esters of 2- and 4-hydroxyestradiol. 2-Hydroxyestradiol 2, 3-dibenzoate was ineffective in the pituitary gland up to a dose of 132 μg/ animal, whereas 4-hydroxyestradiol dibenzoate was equi-potent to estradiol benzoate, showing a maximal induction of progestin binding sites at single doses in the range of 13.2–26.4 μg/animal (equivalent to 10–20 μg of estradiol benzoate). As compared to the pituitary gland, the uterus was much more sensitive to the systemic administration of estrogen benzoates. At single doses in the range of 1.32–6.6 μg/animal (equivalent to 1–5 μg of estradiol benzoate), 4-hydroxyestradiol dibenzoate induced maximal levels of progestin receptors and even 2-hydroxyestradiol dibenzoate, when given at a high dose (132.4 μg/animal, equivalent to 100 μg of estradiol benzoate), produced a slight increase in progestin binding sites.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 100 (1974), S. 115-120 
    ISSN: 1432-072X
    Keywords: Chlorobium ; Adenylyl Sulfate Reductase ; Sulfur Metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Adenylylsulfate reductase was purified from Chlorobium limicola. The most important properties of the enzyme were compared with those of APS reductases from Thiocapsa, thiobacilli and sulfate-reducing bacteria.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. l Glucocorticoid receptor binding of 17/3-carboxamide derivatives of dexamethasone. Livers from adrenalectomised male rats (Wistar, 250 g) were homogenised in buffer containing 20 mM Tris, 20 mM 2-mercaptoethanol, 3 mM MgCl2 and 20% glycerol, pH7.5. The homogenate was centrifuged at 105,000g ...
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The dicyclohexane derivatives shown in Table 1 were synthesised by catalytic perhydrogenation of diethylstilboestrol (III, V) or of mesohexestrol (IV). Chromic oxidation of these diols yielded the corresponding diketones (I, II). All compounds were purified and characterised as part of a project on ...
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  • 6
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Gonadectomy of male rats led to a threefold increase of 3α-hydroxysteroid dehydrogenase (3α-HSDH) activity in pituitary homogenates that could be completely reversed by chronic administration of estradiol or 5α-dihydrotestosterone (DHT). 3α-HSDH was found to be distributed mainly between the 10,000 g and 100,000 g sediments from whole homogenates. The microsomal enzyme activity showed a substantial specificity for NADH whereas the cytosolic enzyme (100,000 g supernatant) demonstrated a slight preference for NADPH. The changes in Vmax found in homogenates following gonadectomy and gonadal steroid administration reflected changes in NADH- linked activity of the microsomal, but not the cytosolic enzyme. Estradiol-induced suppression of NADH-linked 3α-HSDH activity in pituitary homogenates from gonadectomized rats of either sex was accompanied by a similar suppression of NADPH-linked 5α-reductase activity and a marked decrease of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release. In the ovariectomized rat chronic administration of nonsteroidal antiestrogens had strong estrogenic effects on 3α-HSDH activity and LH release, but not on 5α-reductase activity and FSH release. In the gonadectomized male rat, which was much less sensitive to intrinsic estrogenicity of the antiestrogens tested, nafoxidine completely blocked estradiol-induced suppression of 5α-reductase activity and FSH release and partially antagonized suppression of LH release. The trans-isomeric, substituted triphenylethylenes, tamoxifen, and enclomiphene, as well as nitromifene (mixture of trans and cis isomers) were able partially to counteract estradiol-induced suppression of 5α-reductase, but not 3α-HSDH activity. It is concluded that estradiol action on pituitary 5α-reductase, but not 3α-HSDH activity, involves an estrogen receptor mechanism.
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