Quantitative analysis of cellular glutathione in early preimplantation mouse embryos developing in vivo and in vitro

The relative levels of reduced glutathione (GSH) have been measured fluorimetrically in individual eggs and early embryos from two mouse strains, one of which shows developmental arrest in vitro. GSH levels fell by approximately 20-25% at fertilization and by approximately 45% by the late 2-cell and early 4-cell stages. No differences were observed between strains or between embryos cultured in vitro or in vivo. Addition of exogenous H2O2 or diethylmaleate depleted GSH. GSH levels were not affected significantly after inhibition of GSH-peroxidase by mercaptosuccinate nor of catalase by aminotriazole. Mercaptosuccinate did not inhibit development but catalase inhibition caused arrest at the 2-cell stage. Addition of exogenous GSH or thioredoxin did not promote development of 'blocking' embryos through the 2-cell block. It is concluded that early embryos lack a mercaptosuccinate sensitive peroxidase activity for removing H2O2, which may be removed by catalase or the glutathione-S-transferase system. It is suggested that GSH may have a role in detoxifying peroxidated lipids. The results are consistent with a role for reactive oxygen species in the 2-cell block.