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Human endometrial cells in primary tissue culture: modulation of the progesterone receptor level by natural and synthetic estrogens in vitro.

Primary cultures of human endometrial cells were prepared from surgical biopsy specimens (premenopausal) and used to examine the direct regulatory effects of estrogen on the progesterone receptor (PR) level in vitro. Cells were grown as monolayer cultures in Dulbecco's modified Eagle's medium with 10% steroid-depleted serum from castrate adrenalectomized calves. Maximal stimulation of the PR level was obtained after a 3- to 4-day incubation with 10 nM estradiol. A dose-dependent increase in PR was produced by estradiol, with half-maximal stimulation at 1 nM added hormone and optimal increases (up to 7-fold) at 10 nM. The PR had a Kd of 2.5 ± 0.4 × 10−10 M, as determined by Scatchard analysis using17,21-dimethyl-19-norpregna- 4,9-diene-3,20-dione ([3H]R5020), and sedimentedpredominantly as a 7S species on low salt sucrose density gradients. Estrogen stimulation increased the number of progestin-binding sites without altering the receptor affinity. A variety of estrogens, including the synthetic zearalanol ...