In the present studies, we demonstrated successful development to term after transfer of morulae and early blastocysts that were fertilized in mR1ECM-BSA containing 110 mM NaCl and developed in a chemically defined medium, mR1ECM. However, the litter size was very small, and more than half the recipients had failed to maintain the pregnancy around Days 13-20. Similar results were obtained after transfer of morulae or early blastocysts that had been fertilized in vivo and in vitro and then developed in mR1ECM. Therefore, the small litter size and low efficiency of offspring production after transfer of the embryos appear not to be due to unsuitable conditions in mR1ECM-BSA containing 110 mM NaCl, but possibly in mR1ECM. In porcine embryos, both the number of cells in a blastocyst and the incidence of blastocysts hatched were dramatically improved by supplementation with fetal bovine serum by the morula stage. Those characteristics of the embryos were not examined in the present studies. Further investigation will be required to improve the development of rat embryos cultured in mR1ECM and then transferred. buy cipro
In summary, successful sperm penetration has been achieved in a suitable culture medium for rat embryos, mR1ECM, with modifications in which PVA was replaced with BSA and the NaCl concentration was increased to 100-130 mM. Although rat zygotes appear to be very sensitive to the culture condition(s) during pronuclear formation, the developmental ability of the zygotes is maintained in mR1ECM with BSA instead of PVA and containing 110130 mM NaCl. In vitro fertilization in the medium and then early embryonic development in mR1ECM should be a suitable system for production of blastocysts in vitro from rat oocytes.