Exposure of neonatal mice to steroids: Longterm effects on the mammary gland and other reproductive structures

Mice exposed perinatally to various steroid hormones, individually or in combination with other hormones, are being used as an experimental model relevant to clinical observations on the occurrence of vaginal cancer in the human female exposed during fetal life to diethylstilbestrol administered to the mother. Responses of the vagina and mammary gland of female BALB/cfC3H/Crgl mice to neonatal treatments with estradiol, testosterone, progesterone, and estradiol-progesterone combinations are being compared. The steroids result in an earlier age of onset and a higher incidence of mammary tumors in these mammary tumor virus-bearing mice. If ovariectomy is performed at 40 days of age, no mammary tumors develop, thus indicating that ovary-independent alterations are not induced in the mammary gland, as they are in the vagina, by high doses of estrogen or androgen administered neonatally. Progesterone (100 μg per day for the first five days of life) does not induce ovary-independent vaginal cornification and reduces the occurrence of this phenomenon when given simultaneously with estradiol.