Characterization of a progestin-binding component in lactating rat mammary glands |
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Authors: | Masaaki Hirose Masatoshi Maki Hideo Chiba |
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Institution: | 1. Department of Food Science and Nutrition, Nara Women''s University, Nara 630, Japan;2. Department of Food Science and Technology, Kyoto University, Kyoto 606 Japan |
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Abstract: | Experiments were carried out to identify progestin-binding receptors in the mammary gland where casein synthesis is known to be inhibited by this hormone. A progestin-binding component with high affinity, low capacity and a sedimentation coefficient of 8.8 S was isolated from the cytosol of lactating rat mammary glands. This component strongly bound 3H]R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione) with a dissociation constant of 3.9 · 10?9 M under low-salt conditions and with that of 8.2 · 10?10 M in the presence of 0.3 M KCl. Specificity studies showed a higher degree of progestin specificity under high salt conditions. In the absence of KCl, binding of 3H]-R5020 was inhibited by unlabeled glucocorticoid in the same degree as unlabeled progestin, but the inhibition by glucocorticoid was greatly diminished by the presence of 0.3 M KCl. These observations suggest that the 3H]R5020-binding-component is the progestin receptor and that its function may be regulated by the concentration of glucocorticoid and salt. |
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Keywords: | Progestin binding Progesterone receptor Lactation (Rat mammary gland) PPO 2 5-diphenyloxazole POPOP 1 4-bis(5-phenyloxazoyl-2)-benzene |
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