Mammary Gland Development in the Hypophysectomized Albino Rat. ∗

Numerous investigations on mammary gland development in recent years have indicated that the ovarian hormones, estrone and progestin, are responsible for the growth of the glands. However, since increasing knowledge of the physiology of the pituitary gland seems to give it a central position in the endocrine system, investigators have become interested in determining whether or not the mammary glands could be experimentally developed in hypophysectomized animals.

Pencharz and Long 1 who hypophysectomized rats in late pregnancy (20th and 21st days) concluded that mammary development continued in the absence of the pituitary. However, at this stage of pregnancy growth is complete and lactation is being initiated. In fact, Selye, Collip and Thomson 2 observed that milk secretion always set in normally after parturition, but stops after a few hours, in rats hypophysectomized during the latter half of pregnancy. The mammary glands of rats hypophysectomized during the second half of pregnancy have been studied cytologically by Jeffers. 3 The epithelial cells were observed to resemble those of glands from normal pregnant animals. These studies appear to indicate that the development of the mammary gland which normally occurs during the second half of pregnancy can continue in the absence of the pituitary. However, lactation fails within a few hours after parturition. Selye, Collip and Thomson 4 found that the continued application of large doses of estrone in lactating rats failed to lead to repair of the rapid involution of the mammary gland which takes place after hypophysectomy. They were of the opinion that the presence of the pituitary gland is necessary for the action of estrone upon the mammary glands.