Simple induction of pseudopregnancy by artificial stimulation using a sonic vibration in rats.

Embryo transfer has been used as one of the essential reproductive technologies for production of new strains and maintenance of genetic resources in animals. Mating with vasectomised male rats is a requirement for inducing pseudopregnancy in female rats selected for embryo transfer. Although this procedure has been used routinely, large breeding space and high expenditure are required to maintain a sufficient number of females and vasectomised males. This study was performed to induce pseudopregnancy in females by artificial stimulation using sonic vibration instead of vasectomised males. The females continued to be in the dioestrus stage for at least 14 days after artificial stimulation was performed. Of fresh 2-cell embryos that transferred into the oviducts of females after artificial stimulation, 56% was implanted and 50% was developed to offspring. Approximately 46% of the frozen 2-cell embryos were implanted and 24% developed into offspring. Furthermore, 66% of the fresh pronuclear embryos were implanted and 60% developed into offspring. This study successfully induced pseudopregnancy in rat females by artificial stimulation using a sonic vibration. This method, 'Easy-ET', was useful for efficient production and maintenance of rat strains.

Differential regulation of receptivity in two uterine horns of a recipient mouse following asynchronous embryo transfer.

Receptivity is a limited time in which uterine endometrium can establish a successful dialogue with blastocyst. This study was to investigate the effect of asynchronous embryo transfer on uterine receptivity in mice. Embryos under different stages were transferred into two oviduct sides of a recipient mouse on day 1 of pseudopregnancy. Our results showed the asynchronously transferred embryos can implant in all groups. Compared to zygote-transfer group, the length of implanted embryos is longer in 8-cell embryo- or blastocyst-transfer group. The levels of Snail and COX-2 immunostaining in blastocyst-transfer group are significantly stronger than that in zygote-transfer group. Embryos in blastocyst-transfer group migrate faster than that in zygote-transfer group within uterus. Blastocysts are in a state of developmental delay after they are transferred into oviducts, and they are reactivated and implanted rapidly in uterus. The developmental rate to newborn in zygote-transfer group is obviously higher than that in blastocyst-transfer group, suggesting that a delay in embryo development and implantation will lead to a decrease of litter size. These results indicated that the window of implantation is differentially regulated in two uterine horns of a recipient by embryos at different stages.