Presence of amino acids and insulin in a chemically defined medium improves development of 8-cell rat embryos in vitro and subsequent implantation in vivo

This study examined the effects of some components in a chemically defined medium on rat 8-cell embryo development in vitro. The basal medium was a modified culture medium for in vitro fertilization of rat oocytes, containing inorganic salts and energy substrates. After 36 h in culture, 28.8% of the 8-cell embryos developed into blastocysts in the basal medium. This percentage was increased by supplementing the basal medium with free amino acids, but not a premix of insulin/transferrin/selenium (ITS). However, ITS synergized the beneficial effect of amino acids. The beneficial effect of free amino acids could not be duplicated by bovine serum albumin. The synergistic action of ITS was primarily due to insulin. The removal of glucose and/or phosphate from the culture medium had no effect on embryo development in vitro. After transfer to unilaterally pregnant rats, 23.1% of the blastocysts formed in the basal medium developed to Day 18 fetuses, compared to 64.3% for those formed in the medium containing amino acids. These data indicate that the presence of amino acids in the culture medium is beneficial for embryo development in vitro and for implantation and fetal development following transfer to pregnant recipients.