Currently, more than 80% of 1-cell rat embryos can develop to the blastocyst stage in a chemically defined mR1ECM. However, the developmental ability of 1-cell rat embryos in mR1ECM is known to be very low when obtained soon after penetration in vitro. This phenomenon has also been described in hamster embryos in a chemically defined medium, HECM-3. The low early embryonic development was also observed when rat zygotes were collected before pronuclear formation and then cultured in mR1ECM. Low embryonic development appears to be due to the absence of essential factor(s) in mR1ECM during pronuclear formation. The low development of the embryos has been overcome by supplementation of HECM-3 with hypotaurine in the hamster and by preincubation in mKRB. flovent inhaler
In the present studies, the developmental ability of 1-cell rat embryos fertilized in mR1ECM-BSA containing 110-130 mM NaCl was not reduced but improved as compared to that of embryos fertilized in mKRB. Therefore, these results indicate that the factor(s) affecting the developmental ability of embryos during pronuclear formation and missing in mR1ECM was the presence of BSA and/or relatively high NaCl concentrations. Further studies are being directed toward the potential roles of BSA and/or relatively high NaCl concentrations during early development of the zygotes. According to Miyoshi et al., only 45-64% of embryos fertilized in mKRB could develop to the blastocyst stage even when transferred from mKRB to mR1ECM at 5-30 h after insemination. In the present studies, we also demonstrated that more than 80% of embryos fertilized in mR1ECM-BSA containing 110-130 mM NaCl were able to develop to the blastocyst stage. Therefore, this evidence also suggested that factor(s) in mKRB had still reduced the developmental ability during sperm penetration and/or pronuclear formation.