Metabolism of endogenous and exogenous reproductive hormones

Abstract

Estradiol and progesterone are produced in abundance by the ovary of the reproductive-age female (and by the placenta in pregnancy). Serum levels of both hormones are very low in the postmenopause, and indistinguishable from women who have undergone castration. Postmenopausal women have higher levels of aromatase in skin and adipose and convert androstenedione to estrone more effectively than younger women. Estradiol is well absorbed orally, but undergoes extensive first-pass effect resulting in production of the less potent metabolites estrone and estrone sulfate. Ethinyl estradiol is well absorbed, potent, and has more pronounced effects in the production of important hepatic proteins. Progesterone is absorbed orally only if ingested in a micronized form, has a relatively short serum half-life, and is metabolized to products with little biologic activity. The synthetic progestogens are abundant in number; potent in effect; and well absorbed orally, vaginally, and transdermally. New formulations of estrogens and progestogens and new delivery systems promise to provide gynecologists and patients with a long list of potential solutions to contraceptive needs and alternatives for hormone replacement therapies.