In vitro induction of prolactin production and aromatase activity by gonadal steroids exclusively in the stroma of separated proliferative human endometrium

Abstract

Prolactin production by decidualized human endometrium has been demonstrated in organ explant cultures and presumed to be of stromal origin by immunocytochemistry and the presence of simultaneous stromal histologic changes. To test the hypothesis that endometrial prolactin production is exclusively of stromal origin, late proliferative human endometrium was separated into glands and stroma and cultured for 3 days. Confluent cultures were incubated with progesterone, 50 ng/ml; estradiol, 5 ng/ml; or both progesterone and estradiol for 4, 8, and 15 days. Prolactin concentration was measured at 2-day intervals by specific radioimmunoassay throughout a 15-day culture in all samples. Aromatase activity at 15 days was assayed by the production of tritiated water from 1 beta 3H-androstenedione. Possible contamination of gland cultures by stromal cells was controlled by the substitution of D-valine in the culture media. No prolactin was detected in the D-valine-treated gland cultures. Stromal cell cultures demonstrated increasing prolactin with continuous incubation with progesterone (15-day control: 11.28 +/- 0.91 ng/100 micrograms deoxyribonucleic acid versus 15-day progesterone: 245.8 +/- 4.24 ng/100 micrograms). Prolactin levels increased after progesterone was removed at day 4 and 8, reaching peak production 4 days later, followed by a steady decline. Estradiol induced a sustained increase in prolactin production even after withdrawal of steroids. Aromatase activity in gland cells exposed to steroids exhibited no change with time. Steroid-treated stromal cell cultures showed an increase in aromatase activity in all 15-day (controls: 21.6 +/- 0.7 pmol substrate converted per mg of deoxyribonucleic acid per 24 hours versus progesterone: 43.4 +/- 4.2 versus estradiol: 34.2 +/- 3.5 versus progesterone and estradiol: 47.5 +/- 2.4) but not in 4- or 8-day incubations. These studies support these conclusions: (1) nongestational endometrial prolactin is of stromal, not glandular origin; (2) stromal prolactin production is induced and maintained by progesterone: (3) stromal prolactin production is induced by estradiol but does not require continued exposure for maintenance; (4) aromatase activity is increased by long-term exposure to progesterone and estradiol in stroma but not in glands.