Table 2.
Effects of E2 on the duration of the window of uterine receptivity for implantation
| Treatment (E2, ng per mouse)
|
No. of recipients | No. of blastocysts transferred | No. of mice with ISs (%) | No. of ISs (%) | No. of blastocysts recovered from mice without ISs (%) | |
|---|---|---|---|---|---|---|
| Day 7 (1st injection of E2, ng) | Day 8 (2nd injection of E2, ng) | |||||
| 1.5 | 0 | 5 | 74 | 0 | 0 | 19 (26) |
| 1.5 | 4 | 49 | 3 (75) | 19 (39) | 0 | |
| 3.0 | 7 | 92 | 7 (100) | 28 (30) | ||
| 3.0 | 0 | 4 | 46 | 1 (25) | 8 (17) | 0 |
| 3.0 | 10 | 146 | 9 (90) | 49 (34) | 0 | |
| 10.0 | 4 | 56 | 4 (100) | 15 (27) | ||
| 10.0 | 0 | 3 | 37 | 1 (33) | 1 (3) | 1 (7) |
| 3.0 | 6 | 84 | 0 | 0 | 0 | |
| 10.0 | 8 | 94 | 2 (25) | 6 (6) | 3 (19) | |
| 25.0 | 3.0 | 6 | 84 | 0 | 0 | 14 (17) |
| 25.0 | 4 | 48 | 0 | 0 | 5 (10) | |
The recipient mice were ovariectomized on day 4 of pseudopregnancy (0900 hours) and injected daily with P4 (2 mg per mouse) to induce the condition of delayed implantation. On day 7, the recipients received the first injection of E2 at 1.5, 3.0, 10.0, or 25.0 ng. On day 8, day-4 normal blastocysts were transferred into these recipients immediately followed by a second injection of the vehicle (oil) or E2 at 1.5, 3.0, 10.0, or 25.0 ng. Implantation sites (ISs) were examined 48 later. The uteri without implantation sites were flushed to recover unimplanted blastocysts. The IS rate in mice receiving the first E2 injection at 1.5 or 3.0 ng followed by the second injection of 1.5, 3.0, or 10.0 ng of E2 was significantly higher (P < 0.001) than those receiving the first E2 injection at 10.0 or 25.0 ng.