Inhibitory Effect of Estrogen on Mammary Growth and Its Counteraction by Pituitary Isograft in Mice

Abstract

Mammary growth was markedly inhibited in mice by a single subcutaneous injection of 100μg hexestrol dicaprylate despite the fact that the pituitary prolactin levels were significantly higher in these mice than in the intact controls. The degeneration of mammary gland was completely counteracted by the simultaneous isologous pituitary grafting, indicating that the additional supply of prolactin from the grafts overcame the inhibitory action of estrogen on mammary growth. These results have demonstrated the existence of antagonistic effects between prolactin and estrogen on mammary growth in mice at some dose levels of estrogen.