Induction of Mammary Growth in Rats by Estrogen and Progesterone. ∗,†

Summary

The administration of estrogen and progesterone to castrate female rats for 15 days or more stimulated an increase of DNA comparable to that found at a corresponding period of pregnancy. Continued injection of these hormones for periods up to 32 days increased only slightly the DNA content. This is interpreted as indicating a cessation of further gland proliferation even in the presence of these hormones. In the hormone stimulated glands the PNA content increased comparable to pregnancy but since profuse lactation was not stimulated it did not increase compared to the latter stages of pregnancy or lactation. However, when the hormones were administered for 26 days and then stopped, lactation set in sufficient to nourish foster litters of rats.