The nuclear estrogen receptor level and the synthesis of the cytosolic progesterone receptor induced by estradiol

Abstract

The synthesis of the cytosolic progesterone receptor (RcP) in uterus is known to be induced by estradiol (E2) and can be used as a marker for estrogen action. In this study the RcP level is compared with that of nuclear estrogen receptors (RnE) in the uterus of ovariectomized rats, after a single injection of 5 μg E2/kg. The rats were killed from 2 to 72 hr after injection and the uterine RcP was measured in cytosol by 3H-progesterone exchange assay, while the RnE content in crude nuclear suspensions by 3H-estradiol was measured by exchange assay. The RnE content increased 2 hr after injection and remained significantly higher than the control value to 72 hr. The RcP level increased linearly from 2 to 48 hr after injection, coinciding with the high RnE level, and declined later when RnE lowered. These results suggest that the synthesis of RcP is dependent on the retention time of a significant amount of RnE.