The antiprogesterone steroid RU 486: a short pharmacological and clinical review, with emphasis on the interruption of pregnancy.

In this review we have briefly outlined the clinical applications and mechanism of action of the progesterone antagonist RU 486. RU 486 has been successfully used in a variety of conditions to regulate the reproductive cycle and to control fertility in women. We suggest that the mechanism by which RU 486 acts during the cycle and early pregnancy is probably by affecting mainly the endometrium. During late pregnancy, the compound has significant effects on the myometrium including the induction of gap junctions between myometrium cells, which is required for muscle contractility during labour. The use of RU 486 has helped to demonstrate that progesterone is required for maintenance of the late stages of pregnancy in women.