170 The effects of linoleic and linolenic acid supplementation on the in vitro maturation of pig oocytes in a heat-stressed environment

Abstract

Elevated environmental temperatures induce heat stress, which can cause a depression in fertility and early embryonic development. Fatty acids initiate an endergonic reaction that is able to absorb cellular heat, causing a decrease in intracellular temperature. Supplementing linoleic and linolenic acids to the maturation medium of pig oocytes at elevated temperatures reduces the effects of heat stress-induced damage during fertilization and embryonic development. However, the mechanism of action of fatty acids during oocyte maturation is unknown. Therefore, the objective of this study was to minimize heat stress-induced damage and characterise the intracellular oocyte mechanisms. Oocyte maturation media was supplemented with linoleic and linolenic acid during oocyte maturation at either 38.5 or 41.5°C. Oocytes (n = 3094, r = 5) were supplemented with 50 μM linoleic acid, 50 μM linolenic acid, 25 μM of both, or 50 μM of both during 40 to 44 h of maturation and then evaluated for the formation of reactive oxygen species (n = 239), intracellular glutathione concentrations (n = 1005), glutathione peroxidase (n = 1005), catalase (n = 987), and superoxide dismutase (n = 863) activities. Data were analysed using ANOVA with the main effects including treatment, well, and replicate. There were no significant differences between the treatment groups matured at 38.5°C when comparing reactive oxygen species generation. Supplementation of linoleic or linolenic acid significantly decreased (P < 0.05) reactive oxygen species generation in oocytes matured at 41.5°C compared with no supplementation at the same temperature. Supplementation of linoleic or linolenic acid or both significantly increased (P < 0.05) intracellular glutathione concentrations compared with no supplementation at 38.5°C (23.37 ± 1.23 pmol/oocyte) and 41.5°C (10.42 ± 1.01 pmol/oocyte). There were no significant differences between the treatment groups matured at 38.5°C or 41.5°C when comparing glutathione peroxidase activity. Supplementation of linoleic or linolenic acid or both significantly increased (P < 0.05) catalase and superoxide dismutase activities compared with no supplementation at 38.5°C and at 41.5°C. Superoxide dismutase activity was significantly higher (P < 0.05) in oocytes matured at 41.5°C compared with those matured at 38.5°C. These results indicate that supplementing linoleic and linolenic acid to the maturation medium of pig oocytes at an elevated temperature reduces the effects of heat stress-induced damage by increasing intracellular glutathione concentrations and catalase and superoxide dismutase activities.