Hormonal regulation of uterine epithelial cell proliferation. II. Effects of estradiol and progesterone administered in combination.

The effects of estradiol (E2) and progesterone (Pg) administered in combination on the cell proliferation of the ovariectomized B6D2F1 mouse uterine epithelium were assessed by thymidine autoradiography. In the luminal and glandular cell populations Pg inhibits the mitogenic effect of E2 when administered simultaneously or 24 hours after E2; when Pg is given 12 hours after E2 it does not block but slows down the proliferative effect of E2, at least at the concentrations studied here. Given prior to E2, Pg rather exerts an additive (synergistic) effect on uterine epithelia. It is concluded that Pg can exert different actions on the E2- mitogenic effect induced at both luminal and glandular levels. Further investigations are needed to understand better the precise biochemical mechanisms involved in the modulating actions of these steroids on the mouse endometrium epithelial cells.