Estrogen synthesis in human endometrial epithelial glands and stromal cells

Biosynthesis of estrogen was studied in human endometrial epithelial glands and stromal cells. Intact epithelial glands and stromal cells were isolated from human normal proliferative and secretory endometrial specimens. The isolated glands and stromal cells were separately incubated with 10 nM [3H]testosterone in nutrient medium for 20 h in an incubator. Only estrone and estradiol were formed in stromal cells and in epithelial glands in the proliferative phase. Four types of estrogens: estrone, estradiol, estrone sulfate and estradiol-3-sulfate were isolated from the secretory epithelial glands. The capacity of aromatization is higher in stromal cells than that in glands. The highest capacity of aromatization was found in stromal cells in the proliferative phase, 58 +/- 30 fmol/mg protein (means +/- SD, n = 10) followed in order by stromal cells in the secretory phase, 30 +/- 18 (n = 6), and the epithelial glands in the proliferative and secretory phase, 22 +/- 12 (n = 10) and 4.3 +/- 1.2 (n = 6), respectively. These results indicate that the aromatase in endometrium is distributed in both stromal cells and epithelial glands. The capacity of aromatization varies in the 2 phases of the menstrual cycle with a significant decrease in activity of the epithelial glands in the secretory phase. The capacity of aromatization was also examined when stromal cells were incubated with various concentrations of [3H]T. The apparent Km, estimated from the concentration of delta 4-androgens in cells, is about 27 nM, indicating that the endometrial aromatase has a considerably high affinity to delta 4-androgens.