Cytoplasmic estrogen receptors of rat mammary glands during pregnancy and puerperium.

Abstract

The variation of cytoplasmic estrogen receptor in the mammary gland during pregnancy and puerperium was studied to determine the role of estrogens in the mechanism of lactation. Cytosol estrogen receptors from rat mammary glands were incubated with 3H-estradiol, and the free estradiol was removed using dextran-coated charcoal. The maximum number of binding sites in the cytosol was estimated from saturation curves and Scatchard analysis. During pregnancy the number of binding sites was relatively low (2.5 to 3.8 pmoles per mg protein), but increased after delivery to 7.8 pmoles per mg protein. The number of estrogen binding sites in the mammary glands of lactating rats five days after delivery was at the same level as on the day of delivery. However, at ten days after delivery the number of binding sites increased markedly to 58.9 pmoles per protein. The number of estrogen-binding sites in the mammary glands of lactating rats was decreased by castration and by the injection of testosterone or 2-bromoergocriptine. There appeared no competition by testosterone, progesterone or cortisol with estrogen receptors in the mammary gland.