Cold culture of different stage mouse embryos in bicarbonated and bicarbonate-free media

Abstract

Mouse embryos of different stages of development were cultured to expanded blastocysts following storage (1 to 8 d) at 4°C in the presence or absence of HCO 3 −. The effect of oxygen tension on the cold storage of one- and two-cell mouse embryos at 4°C was evaluated by 37°C culture and transfer to pseudopregnant recipients. Survival at 4°C of early, one- to four-cell mouse embryos was improved with HCO 3 − in the medium. The presence of HCO 3 − was not of benefit for morulae or blastocyst survival following cold storage. Reducing the oxygen atmosphere from 20 to 5% O 2 improved survival of one-cell mouse embryos stored at 4°C. The survival of two- and four-cell embryos, morulae and blastocysts at 4°C was similar in 90% N 2, 5% CO 2 and 5% CO 2 in air, but it was significantly poorer in air alone. The collapse of morulae and blastocysts during cold storage up to 5 d was reduced with HCO 3 − in the storage medium. Blastocysts stored for 6 d at 4°C failed to survive following immediate transfer to pseudopregnant recipients. Blastocyst survival was improved compared to controls (direct transfer of unstored blastocysts to recipients) when cultured for 36 h at 37°C following 6 d of cold storage. This result suggests that cold-stored mouse blastocysts may require a metabolic period of readjustment to survive following transfer to synchronized recipients.