Exposure to L‐Ascorbic Acid or α‐Tocopherol Facilitates the Development of Porcine Denuded Oocytes from Metaphase I to Metaphase II and Prevents Cumulus Cells from Fragmentation

Contents It is known that α-tocopherol (vitamin E) and l-ascorbic acid (vitamin C) can modulate many biochemical processes intracellularly or extracellularly as antioxidants. The objective of the present study was to investigate the effects of α-tocopherol and l-ascorbic acid on porcine oocyte meiotic maturation, viability and the functions of cumulus cells. In two independent experiments, porcine oocytes with or free from cumulus cells were exposed to different levels of α-tocopherol (0, 10, 100 and 200 μm) or l-ascorbic acid (0, 50, 250 and 750 μm). Cumulus expansion, cumulus cell DNA fragmentation, meiotic maturation and degeneration of oocytes were assessed 48 h after in vitro culture. The results showed that: (1) neither α-tocopherol nor l-ascorbic acid influenced cumulus expansion but both prevented cumulus cell DNA fragmentation. (2) α-tocopherol lowered the percentage of denuded oocytes (DOs) arrested at germinal vesicle stage (GV). Among the oocytes undergoing germinal vesicle breakdown (GVBD) proportion, fewer DOs treated by α-tocopherol were at metaphase I (MI) and more at metaphase II (MII). l-ascorbic acid caused lower percentage of DOs arrested at GV stage and higher percentage of DOs undergoing GVBD, especially at MII. The influences of α-tocopherol and l-ascorbic acid were not obvious in cumulus-enclosed oocytes (CEOs). (3) Both vitamins compromised the viability of CEOs and DOs. These results indicate that exposure to α-tocopherol or l-ascorbic acid promotes the development of porcine DOs from MI to MII and prevents cumulus cell DNA fragmentation at certain levels, especially 10 μmα-tocopherol or 250 μml-ascorbic acid.