Mouse embryo cleavage, metabolism and viability: role of medium composition

The cleavage, metabolism and viability of mouse zygotes wereassessed after culture in media of different ionic and metabolitecomposition. Medium with a high potassium concentration, characteristicof mammalian oviduct fluid, inhibited cleavage and blastocystformation (P < 0.01). This inhibition was partially alleviatedby the removal of phosphate, and subsequently abolished by supplementationwith amino acids, vitamins, insulin, epidermal growth factorand transferrin (AVIET). Glucose uptake by cultured blastocysts,measured fluorimetrically, was not affected by the ionic ormetabolite composition of the medium, but was significantlyreduced by the inclusion of AVIET (P < 0.01). Lactate productionwas also significantly reduced in the presence of AVIET (P <0.01). Calculations of metabolic activity revealed that embryoscultured in the presence of AVIET had a glycolytic activitysimilar to embryos developed in vivo. In contrast, embryos culturedin conventional embryo culture media exhibited an elevated glycolyticactivity. Culturing embryos for 4 days in a reduced lactateconcentration (4.79 mM), significantly increased fetal developmentafter transfer, compared with embryos cultured in the concentrationof lactate present in conventional embryo culture media (23.3mM; P < 0.01). In contrast, when embryos were transferredon day 3 of culture, significantly more fetuses were obtainedfrom embryos cultured in high levels of lactate (P < 0.01).Supplementation of medium with AVIET significantly increasedresultant fetal weights after transfer (P < 0.05). This studydemonstrates that different media are required to maintain embryoviability on successive days of culture, and highlights thepotential limitations of employing simple salt solutions forthe culture of preimplantation mammalian embryos.