Effects of Hormones and 7,12-Dimethylbenz- [a]anthracene on Rat Mammary Tissue Grown in Organ Culture 1,2

SUMMARY-Mammary glands from 50- to 60-day-old female Sprague-Dawley rats were cultivated for 6-12 days in a synthetic medium supple-mented with insulin, estrogen, cortisol, progesterone, and prolactin, singly or in different combinations. Insulin was essential for maintenance of the glands in culture. Of all the other hormones studied, progesterone greatly stimulated mammary gland explants. This stimulation, as measured by labeling index and mitotic index, reached a maximum level when insulin, estrogen, prolactin, and progesterone were combined. Progesterone com-bined with insulin alone or with other hormones induced lobuloalveolar development. The increased DNA synthesis resulting from the hormonal stimulation produced by hormone combination, however, did not alter the duration of DNA synthesis. The carcinogenic polycyclic hydrocarbon 7,12-dimethylbenz[alanthracene (DMBA) added in excess of 1 p,g/ml of medium was severely toxic to the mammary epithelial cells. However, 1 J.lg of DMBA/ml of medium, was suitable for our study. DMBA increase