RU486 (mifepristone) has proved to be a remarkably active antiprogesterone and antiglucocorticosteroid agent in human beings. The mechanism of action involves the intracellular receptors of the antagonized hormones (progesterone and glucocorticosteroids). At the molecular level, the most important features are high binding affinity to the receptor, interaction of the phenylaminodimethyl group in the 11 beta-position with a specific region of the receptor binding pocket, and RU486-induced transconformation differences in the ligand-binding domain. These particularities have consequences at different steps of the receptor function as compared with agonists. However, the reasoning cannot be limited to the RU486-receptor interaction, and, for instance, there is the possibility of a switch from antagonistic property to agonist activity, depending on the intervention of other signaling pathways. It would be desirable to have derivatives with only one of the two antagonistic properties (antiprogestin, antiglucocorticosteroid) in spite of similarities between steroid structures, receptors involved, and responsive machineries in target cells. Clinically, the RU486-plus-prostaglandin method is ready to be used on a large scale and is close to being as convenient and safe as any medical method of abortion may be. The early use of RU486 as a contragestive as soon as a woman fears a pregnancy she does not want will help to defuse the abortion issue. Research should now be conducted to define an efficient and convenient contraceptive method with RU486 or other antiprogestins. The usefulness of RU486 for obstetric indications, including facilitation of difficult delivery, has to be assessed rapidly. Gynecologic trials, particularly in leiomyomata, should be systemically continued. The very preliminary results obtained with tumors, including breast cancers, indicate that further studies are necessary.

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The steroid hormones corticosterone and testosterone are supplied to the central nervous system by endocrine glands, the adrenals and gonads. In contrast, the 3 beta-hydroxy-delta 5-derivatives of cholesterol, pregnenolone and dehydroepiandrosterone, accumulate in the rat brain through mechanisms independent of peripheral sources. Immunohistochemical studies have been performed with specific antibodies to bovine adrenal cytochrome P-450scc, which is involved in cholesterol side-chain cleavage and pregnenolone formation. The enzyme was localized in the white matter throughout the brain. Scarce clusters of cell bodies were also stained in the entorhinal and cingulate cortex and in the olfactory bulb. These observations strongly support the existence of "neurosteroids," which have been posited on the basis of biochemical, physiological, and behavioral studies.