Progesterone-induced estrogen receptor-regulatory factor is not 17 beta-hydroxysteroid dehydrogenase

These studies were done to determine if the progesterone-induced estrogen receptor-regulatory factor (ReRF) in hamster uterus is 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD), i.e. that rapid loss of nuclear estrogen receptor (Re) might be due to enhanced estradiol oxidation to estrone catalyzed by 17 beta-HSD. Treatment of proestrous hamsters with progesterone (approximately 25 mg/kg BW) for either 2 h or 4 h had no effect on 17 beta-HSD activity measured as the rate of conversion of [6,7-3H]estradiol to [3H]estrone by whole uterine homogenates at 35 degrees C. During this same time interval, progesterone treatment increased the rate of inactivation of the occupied form of nuclear Re as determined during a 30 min incubation of uterine nuclear extract in vitro at 36 degrees C. Since we previously demonstrated that such in vitro Re-inactivating activity represents ReRF, the present studies show that ReRF is not 17 beta-HSD or a modifier of that enzyme.