Antigestogens.

Antigestogens are compounds which inhibit the synthesis of progesterone or antagonise its biological action. The progesterone antagonist mifepristone (RU 486) binds with high affinity to progesterone receptors throughout the body, blocking the action of endogenous progesterone. In the last 10 years it has been demonstrated that mifepristone, in combination with a suitable prostaglandin, is a safe, effective alternative to vacuum aspiration for termination of pregnancy in the first two months. Preliminary trials suggest that antigestogens may be useful true contraceptives by inhibiting ovulation or by preventing implantation as once a month pills and postcoital agents. In late pregnancy, by sensitising the uterus to prostaglandins and by promoting cervical dilatation, they may induce labour and facilitate lactation. In non-pregnant women mifepristone may have application in the treatment of hormone-dependent conditions such as endometriosis, fibromyomata, meningioma and breast cancer. The availability of hormone antagonists to oestrogens, androgens and progesterone offers the possibility of new methods of regulating reproductive function in health and disease.