Rat Endometrial Cells in Primary Culture: Effects and Interaction of Sex Hormones and Vitamin D3Metabolites on Alkaline Phosphatase

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Abstract
The effects of 2 sex steroids, 17.beta.-estradiol and progesterone, and 2 vitamin D3 metabolites, 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3) and 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on the alkaline phosphatase activity (AP) of cultured endometrial cells of ovariectomized animals and whether the in vitro or in vivo sex steroid pretreatment modifies the cellular AP responses to these vitamin D3 metabolites were investigated. Cells were cultured in Dulbecco''s medium with 10% fetal calf serum until confluency and then for 18 h in a serum-free medium. All subsequent studies were performed in a fresh fetal calf serum-free medium. In endometrial cells from untreated ovariectomized rats, 17.beta.-estradiol (10-9 M) or progesterone (10-9 M) induced increases in AP (40 or 30%) after 2-4 h incubation, respectively. A maximal increasing effect (20%) is observed with 24,25-(OH)2D3 (10-9 M) after 4 h incubation contrasting with the total lack of action of 1,25-(OH)2D3 whatever the concentration (10-13-10-7 M) and the incubation time (1-18 h) tested. After in vivo or in vitro pretreatment with each sex hormone taken separately, both 24,25-(OH)2D3 and 1,25-(OH)2D3 decrease AP whereas after pretreatment with sex steroids in association, these vitamin D3 metabolites induce an increase in AP. Endometrial cell AP is sensitive to 24,25-(OH)2D3 and 1,25-(OH)2D3 and the AP response of these cells is modulated by the presence of 17.beta.-estradiol and/or progesterone.