During the initial stages of gestation, the development of male and female embryos is indistinguishable. At about day 56, hormones become involved. All embryos spontaneously develop into phenotypic females in the absence of a Y-chromosome induced event. The ovaries are bifunctional organs that produce both estrogens and progestins. Establish the milieu required for maintenance of pregnancy. Several synthetic compounds have estrogenic activity. Most modifications were designed to resist hepatic metabolism so that the compounds can be taken orally.
17a-Ethinyl Estradiol and Mestranol are used in oral contraceptives. Numerous compounds with antiestrogenic activity have been synthesized. These antagonists act by competing with estradiol for its intracellular receptor, causing the receptor to assume an inactive conformation. These antagonists are used in the treatment of estrogen-dependent breast cancer and in breast cancer prevention. Hormonal stimulation is known to be a factor in the development and growth of breast carcinomas.