Estrogen receptors in mammary gland primordia of fetal mouse.

Swiss albino mice were injected on day 16 of pregnancy with 3H diethylstilbestrol. Fetuses were sacrificed 3 h afterwards, frozen, and processed for thaw-mount autoradiography. The serial sections from 4 fetuses were studied. Intense nuclear concentration of radioactivity was found in the mesenchymal cells directly surrounding the epithelial primordia of the mammary glands, but not in the epithelium itself. Localization was similar in male and female fetuses. These findings are discussed in relation to their developmental, teratological, and onocological implications.