ANTIANDROGENIC PROPERTY OF RU-486 - ENHANCEMENT OF ESTROGEN-INDUCED UTERINE PEROXIDASE-ACTIVITY IN THE RAT

The contragestational steroid RU 486 enhanced the increase in peroxida se activity produced by estradiol in estrogen-primed immature rat uter i and, like the antiandrogen flutamide, RU 486 reversed the inhibitory effect of testosterone on this estrogen-induced response. It antagoni zed the inhibition produced by progesterone but had no effect on perox idase induction by itself or in unprimed immature animals. RU 486 also enhanced the effect of estradiol on the synthesis of complement compo nent C3 in the rat uterus. The results confirm that RU 486 possesses a ntiandrogenic as well as antiprogestational properties. They also sugg est that, in normal adult animals, the increase in peroxidase activity in the uterus in response to estrogen is not expressed fully but held in check by other endogenous steroids acting through their individual receptors.