Regulation of endometrial endothelial cell proliferation by oestrogen and progesterone in the ovariectomized mouse

Although the endometrial epithelial and stromal cell response to oestrogen and progesterone is well characterized, relatively little is known about the endothelial cell response. The aim of this study was to investigate the time course of endometrial endothelial cell proliferation in response to a specific regimen of oestrogen and progesterone, and to compare it with the stromal and epithelial cell response in mouse endometrium. Adult female mice were ovariectomized to induce endometrial regression. After 7 days, hormonal treatments were given according to the following regimen: days 1-3: 100 ng oestradiol; days 4-6: 10 ng oestradiol and 500 mug progesterone; and day 7: 100 ng oestradiol and 500 mug progesterone. On each day of hormonal treatment, mice (n=5) were injected with bromodeoxyuridine and perfusion fixed 4 h later with buffered formalin. Proliferating endometrial cells were detected by monoclonal antibody against bromodeoxyuridine, and endothelial cells were detected by antibody to CD31. At day 7 after ovariectomy few proliferating cells were found in the endometrium. After 1 day of oestrogen treatment, significant proliferation was detected in the endothelial cells (0.0% versus 16.1+/-1.2%, P<0.001). In contrast to the rapid response of the vasculature, glandular epithelial proliferation increased only after 2 days of oestrogen treatment (7.6±1.3% versus 18.8±2.4%, P<0.05). Progesterone with low dose oestrogen treatment tended to reduce epithelial and endothelial cell proliferation compared with the effect of high dose oestradiol alone. A combination of progesterone with high dose oestrogen induced higher rates of endothelial cell proliferation than did any other treatment (20.8+/-3.2%). These results demonstrate that oestrogen induces rapid proliferation of endometrial endothelial cells, indicating that vascular growth apparently precedes endometrial tissue remodelling. These data also demonstrate that the proliferative response of endometrial endothelial cells to oestrogen and progesterone is different from that of either epithelial or stromal cells.