Effects of neonatally administered sex steroids on 7,12-dimethylbenz(a)anthracene-induced mammary neoplasia in rats.

Female Sprague-Dawley 5-day-old rats were given s.c. either 0.05 ml sesame oil, 1.25 mg progesterone, 0.1 mg estradici benzoate, or 1.25 mg testosterone propionate. At 55 days of age all rats were given 20 mg of 7,12-dimethylbenz(a)anthracene (DMBA) by stomach tube. All rats were killed at 190 days of age. Both the estradiol and the testosterone propionate treatments decreased the mammary adenocarcinoma response to DMBA and increased the mammary fibroadenoma response to DMBA. Both es tradiol benzoateand testosterone propionate-treated rats exhibited fewer developing ovarian follicles and no corpora lutea. Only testosterone propionate-treated rats exhibited lactation. Progesterone treatment increased the mammary adenocarcinoma response to DMBA and was without effect on the mammary fibroadenoma response to DMBA and ovarian structure.