Figure 1.

Schematic diagram of hormonal and surgical regimen used to induce decidual response. The top portion of the figure is a schematic representing the trends in progesterone (P) and estradiol (E) levels in the mouse during the estrous cycle and early pregnancy. Estradiol levels peak just before ovulation during the estrous phase and then drop, but remain above the basal level through the periimplantation period. The progesterone level begins to rise after ovulation and is maintained at a plateau if implantation occurs. To mimic this cycle, animals are given a priming dose of estradiol on days 1, 2, and 3 (E). After 2 days with no injection, mice are treated with progesterone and a low dose of estradiol (PE) on days 6–13. Six hr following the third P injection, the uterine lumen is traumatized as described in the Materials and Methods section to mimic implantation. The tissue is collected and analyzed on the day following the final injection. The hormonal regimen was altered to determine the role of estrogen by excluding estrogen from all injections (no E), or cotreating with antiestrogen ICI 182,780 (anti-E) with all injections.