Estrogen receptors in cultured rat uterine cells: induction of progesterone receptors in the absence of estrogen receptor processing.

When cultured rat uterine cells were treated for up to 6 h with 5 nM 17 beta-estradiol, no decrease in the [3H] estradiol-binding capacity of the cells was observed (i.e. no processing). This was true whether the cells were treated directly with 5 nM [3H]estradiol or with 5 nM unlabeled 17 beta-estradiol followed by homogenization and exchange with [3H]estradiol in vitro. In additional experiments, intact cells were treated with medium containing 5 nM [3H]estradiol for 30 min, and then that medium was removed and replaced with medium containing 5 nM unlabeled 17 beta-estradiol. Receptor-bound estradiol in intact cells was totally exchangeable with estradiol in the culture medium (t1/2, approximately 90 min). Six-hour treatment of cells with 5 nM 17 beta-estradiol led to a 50% increase in the [3H]progesterone-binding capacity of the cells, while no loss of estrogen-binding capacity occurred. These results indicate that progesterone receptors can be induced by estrogen in the rat uterus in the absence of estrogen receptor processing.