Stimulatory effect of clofibrate on the action of estradiol in the mammary gland but not in the uterus of rats.

Treatment of ovariectomized rats with dietary clofibrate caused a manyfold increase in the liver microsomal esterification of estradiol with fatty acids. The stimulatory effect of clofibrate administration on fatty acid esterification of estradiol by liver microsomes was paralleled in vivo by enhanced estradiol-induced increases in the formation of lobules in the mammary gland and by increased incorporation of bromodeoxyuridine into these lobules. In contrast to the stimulatory effect of clofibrate administration on the action of estradiol in the mammary gland, clofibrate administration had no effect on the uterotropic action of estradiol. These results indicate that clofibrate administration has a selective stimulatory effect on the hormonal action of estradiol in the mammary gland but not in the uterus.