Inhibition of proliferation and differentiation by RU 486 in human endometrial stromal and epithelial cells in vitro.

The effects of progesterone and RU 486 on cellular proliferation and differentiation in long term cultures of mixed human endometrial cells were studied. The endometrial tissue was obtained from women with normal menstrual cycles who were undergoing hysterectomy for benign growths. Estradiol supplemented cultures were treated with progesterone and/or RU 486 for 27 days. Cell number was measured by crystal violet assay, and prolactin secretion was used as a marker of differentiation. Progesterone doubled the rate of proliferation, but the addition of RU 486 reduced it to baseline again. The gestagen increased prolactin secretion up to 30 times, while the addition of RU 486 suppressed it to baseline levels. When administered to cells that were pretreated with progesterone for 15 days RU 486 abolished the progesterone effects. RU 486 alone was without any effect. Our results indicate that (1) in vitro progesterone is essential for the initiation and maintenance of proliferation and differentiation of endometrial cells and (2) RU 486 acts as a pure progesterone antagonist in our culture model.