Effects of Cysteine During In Vitro Maturation of Porcine Oocytes Under Low Oxygen Tension on Their Subsequent In Vitro Fertilization and Development

In this study, we evaluated the effect of different concentrations of cysteine in in vitro maturation (IVM) medium during IVM under low oxygen tension (5% O(2)) of porcine oocytes on the intracellular content of glutathione (GSH) and subsequent in vitro fertilization (IVF) and development. Cumulus oocyte complexes (COCs) were collected from ovaries obtained at a local slaughterhouse, cultured in IVM medium supplemented with 0 (control), 0.05, 0.1, 0.2 or 0.6 mM cysteine for 44-46 h, fertilized in vitro and subsequently cultured for 6 days in total. The GSH content of the IVM oocytes exposed to 0, 0.05, 0.1, 0.2 or 0.6 mM cysteine increased significantly (P<0.05) as the concentration of cysteine increased (12.2, 14.0, 15.1, 16.4 and 16.4 pmol/oocyte, respectively). However, the rates of oocyte maturation, sperm penetration, male pronuclear formation, monospermy and even cleavage on Day 2 (the day of IVF was defined as Day 0) and blastocyst formation on Day 6 did not differ among the groups. Moreover, the cell numbers of blastomeres in blastocysts were uniform among the groups. These results indicate that supplementation with 0.05-0.6 mM cysteine during IVM under 5% O(2) tension significantly increased the intracellular GSH contents of IVM oocytes; however, it had no promoting effects on nuclear maturation, fertilization, male pronucleus formation and subsequent embryonic development to the blastocyst stage.