The major estrogen secreted by the ovary is 17β-estradiol; this is converted to estrone in the blood. Estriol is the principal estrogen formed by the placenta during pregnancy. These three compounds, 17β-estradiol, estrone, and estriol, account for most of the estrogenic activity in humans.
The ability of estrogens to suppress secretion of follicle-stimulating hormone (FSH) by the pituitary gland and thereby inhibit ovulation makes estrogen and estrogenlike compounds major components in oral contraceptives. Estrogen replacement therapy (ERT) uses synthetic estrogen (e.g., Premarin), typically given with progestins (e.g., Provera) to treat the physical changes of menopause, including hot flashes and vaginal dryness. ERT also retards the development of osteoporosis in postmenopausal women but increases the risk of breast cancer, heart attack (see infarction), stroke, and, when not given with progestins, uterine cancer. Estrogens are also used to treat prostate cancer.
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