Abstract
Purpose: Using mouse blastocysts with implantation delayed for 7 days (dormant blastocysts) and time-lapse videomicrography, we examined the physiological role of contractions in hatched blastocysts. Methods: The degree and number of contractions in dormant blastocysts were analyzed in images recorded for 48 h of culture, and compared with those in dormant blastocysts in which implantation was induced (activated blastocysts), and dormant blastocysts cultured with estrogen or progesterone. Results: Activated blastocysts exhibited a significantly smaller number of weak contractions and a significantly larger number of strong contractions, compared with dormant blastocysts. Furthermore, the numbers of weak and strong contractions in dormant blastocysts cultured with estradiol-17β were significantly less frequent or more frequent than those in dormant blastocysts cultured with progesterone and those cultured without steroids. Expression of estrogen receptor mRNA was also detected in dormant blastocysts by the method of reverse transcription-polymerase chain reaction. Conclusion: These results suggested that activated blastocysts enhance the contractions as a preparation for the implantation, and that the enhanced contractions in those serve as a physical stimulation for maternal recognition of pregnancy.