Progesterone regulation of prolactin release from human endometrial stromal cells in culture: potential bioassay for progestational activity.

Prolactin was produced by endometrial stromal cells, but not by epithelial cells, in primary culture. Production was stimulated by progesterone in a time and dose (1-1000 nmol/l) dependent way. Stimulation was started one day after plating. The release of prolactin started one day earlier in cultures from luteal phase than proliferative phase endometria. The responsiveness to progesterone declined with time in culture, sooner in luteal than in proliferative phase cultures, but could, at least partly, be maintained by including estradiol (10 nmol/l) in the medium. Lost response to progesterone could be restored by stimulation with estradiol for two days. The results indicate that prolactin synthesis in the endometrium is regulated directly by progesterone, and indirectly by estradiol. We suggest that prolactin production in primary stromal cell cultures could serve as a bioassay for progestational activity of steroid hormones in the human endometrium.