Characterization of a progestin-binding component in lactating rat mammary glands.
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 high 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.
D000818:Animals; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology; D007700:Kinetics; D007774:Lactation; D008321:Mammary Glands, Animal / Q000032:analysis / Q000378:metabolism*; D009649:Norpregnadienes / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011247:Pregnancy; D011372:Progestins / Q000494:pharmacology; D011397:Promegestone / Q000378:metabolism*; D051381:Rats; D011980:Receptors, Progesterone / Q000302:isolation & purification / Q000378:metabolism*
D005938:Glucocorticoids; D009649:Norpregnadienes; D011372:Progestins; D011980:Receptors, Progesterone; D011189:Potassium Chloride; D011397:Promegestone