Effect of oestradiol on progesterone receptors in normal mammary glands and its relationship with lactation.

Mammary glands of lactating mice, either intact or ovariectomized, do not contain detectable amounts of progesterone receptors and this lack of receptors persists also in tissues of animals treated with oestradiol. In contrast with lactators, mammary glands of virgin mice contain progesterone receptors whose amounts are augmented by oestradiol administration.