Local Action of Estrone on Mammary Glands of Mice *

It has been assumed that estrogens act indirectly on the mammary glands because these hormones induce little or no growth of the breast tissues in hypophysectomized animals of most species.5s18 The results, however, have not been entirely uniform.2 Most investigators have noted an absence of mammary growth in those experiments in which hypophysectomized rats and mice have been given estrogens.' 14.1 The simultaneous administration of extract of the hypophysis containing growth-stimulating activity and of estrogen or certain lipoidal fractions of the anterior pituitary gland has resulted in mammary growth in hypophysectomized rats and mice.6'18 These "mammogenic" extracts of the pituitary gland have been assayed by determinations of the mammary development they induce in young male mice.8 The above observations indicate that estrogens act indirectly upon the mammary glands by inducing the pituitary gland to produce a "mammogenic" substance or hormone. The absence of mammary growth in the hypophysectomized animals receiving estrogens is not adequate proof of a direct action of the pituitary gland on the breast tissues. Hypophysectomy results in many other changes in the animal, some of which may affect mammary proliferation. Estrogens are effective in extremely small amounts when applied locally to the vagina.9' 0 Systemic and local reactions occurred when estrogens were applied cutaneously in various solvents or carriers.' 20 The local action of estrogens on the mammary glands has indicated a direct stimulating effect in man, rabbits, and monkeys.11,12'17 The present experiments were undertaken to determine whether estrogens might act locally upon the mammary glands of