INDUCTION OF IMPLANTATION OF BLASTOCYSTS TRANSFERRED TO OVARIECTOMIZED MICE

Abstract

SUMMARY Blastocysts transferred to progesterone-treated ovariectomized mice implanted only if oestradiol was given at or after transfer. A dose of 1·0 m.g. Provera/day maintained the implants to term. Omission of priming with oestradiol did not prevent implantation. Transfers performed on day 0, 1 or 2 of progesterone treatment were completely unsuccessful, while transfers on day 8 were less effective than those performed on day 3 or 4. Administration of oestradiol 24 or 48 hr. beforehand did not prevent the induction of implantation by a second dose of oestradiol, and did not render the uterus 'refractory'. Treatment with 8 ng. oestradiol on days 1 to 5 or day 4 or 5 induced implantation of blastocysts transferred on day 4. It is concluded that oestrogen is not released as a surge before implantation, but is released continuously after ovulation.