Exogenous protein affects developmental competence and metabolic activity of bovine pre-implantation embryos in vitro

The role of exogenous protein during bovine pre-implantation embryo development in two in vitro production systems was investigated. Morphological development, survival after vitrification and metabolic activity before and after vitrification were recorded in blastocysts generated in vitro in synthetic oviduct fluid (SOF) medium in the presence of either bovine serum albumin (BSA) or polyvinyl-alcohol (PVA). Metabolic activity was determined by measuring oxygen consumption, glucose and pyruvate uptake as well as lactate production. Development to blastocysts and survival after vitrification were reduced significantly in medium lacking protein. Of the metabolic parameters measured, only pyruvate uptake was increased significantly in embryos cultured in medium supplemented with PVA. Whereas in BSA-supplemented medium pyruvate uptake was correlated with lactate production, in PVA-supplemented medium glucose uptake was correlated with lactate production. Lactate production increased significantly after vitrification as compared with fresh embryos. Thus, exogenously added protein significantly alters oxidative metabolism. In medium lacking protein, the additional pyruvate may be used for the maintenance of intracellular amino acid pools. Vitrification appears to alter glycolytic metabolic profiles indicating a stress-response. In conclusion, the perturbed metabolism corresponding to reduced developmental capacity of embryos produced under protein-free conditions emphasizes the ambiguity between maximum development, technical and hygienic requirements and physiological demands of the early bovine embryo in vitro. The use of well-defined recombinant proteins might assist in closing this gap.