Effect of estradiol and progesterone on human endometrial aromatase activity in primary cell culture

Isolated human endometrial stromal cells were cultured in RPMI 1640 medium containing insulin, antibiotics and 10% fetal calf serum. After the stromal cells developed a confluent monolayer, estradiol (E2), progesterone (P), or both were separately added to the culture medium and cells were continuously cultured for various periods of time. Aromatase activity was measured in control and hormone-treated cells by incubating the intact cells with [3H]testosterone and isolating the estrogens at the end of incubation. E2 alone did not change the aromatase activity. P caused an 8- to greater than 40-fold increase over the control values (1 to 7 fmol/mg protein X h), and the activity was further increased in the presence of E2 (20- to 100-fold). The stimulation of aromatase activity by P was found to be both time- and dose-dependent and blocked by actinomycin D. Maximal stimulation was reached after the stromal cells were treated with 300 nM P for 3 days. At 30 nM P, a concentration similar to the plasma level during the luteal phase of the menstrual cycle, 80% of maximal stimulation was noted. These results indicate that P stimulates aromatase in endometrial stromal cells and E2 potentiates this stimulation. Much smaller effects of E2 and P on the aromatase activity were noted in endometrial epithelial glands.