Stimulatory effects of insulin on the development of bovine embryos fertilized in vitro

To obtain information about the effects of insulin on the development of bovine embryos, fertilized bovine embryos in vitro were cultured in a chemically defined, protein-free medium: modified synthetic oviduct fluid (mSOF) supplemented with 1 mg/ml polyvinyl alcohol (PVA). The percentage of embryos reaching the morula stage was not affected by the addition of 5 micrograms/ml insulin alone, but insulin showed a beneficial synergistic effect with amino acids (AAs) on the embryonic development to morula. Supplementation of insulin (1-100 micrograms/ml) with mSOF+AAs did not improve the percentage of embryos developing to the blastocyst stage. However, a significant increase in cell numbers of blastocysts was observed with the addition of 1 mM glucose and 1 or 10 micrograms/ml insulin from the morula stage. These results show that insulin has a beneficial effect on the preimplantation development of bovine embryos in the presence of AAs and/or glucose, and suggest that insulin improves embryonic development by stimulating AAs transport and/or glucose uptake.