Effect of Ovarian Extract on Oocyte Maturation and Early Embryonic Development in Pigs

Various factors in the ovary are known to regulate oocyte maturation and hormone secretory functions; however, the effect of ovarian extract (OE) on oocyte maturation and embryonic development in pigs remains unknown. In this study, we first evaluated whether OE supplementation in the in vitro maturation (IVM) medium alters the oocyte maturation capacity by affecting glucose/amino acid metabolites, meiotic maturation, cumulus cell (CC) expansion, and antioxidants. Various OE concentrations (50, 100, 200, 500, and 5000 μg/mL) were included in the IVM medium. Only the oocytes treated with 100 μg/mL OE exhibited an improved meiotic maturation rate when compared with that of the other groups (non-treated group, 78.6 ± 3.0% vs. 100 μg/mL OE-treated group, 81.6 ± 4.3%); however, the difference was not significant. To observe the changes in glucose and amino acid metabolism in the OE-treated oocytes, we measured the amounts of diverse constituents (glucose, lactate, glutamine, and ammonia) in the IVM medium containing OE. Lactate and ammonia levels in the OE-treated group after 44 h of IVM were higher (p < 0.01) than those in the non-treated group. In addition, the expression of the CC expansion factors (Has2 and Tnfaip6) significantly increased (p < 0.05), whereas the mRNA expression levels of antioxidative enzymes (Sod1, Cat, and Gpx1) significantly diminished (p < 0.05) in the OE-treated group. Moreover, mature oocytes treated with 100 μg/mL OE demonstrated increased subsequent embryonic development rates after 144 h of IVM. Thus, the addition of OE in IVM mediums may improve oocyte maturation capacity which could enhance antioxidative enzyme activation, energy metabolism, and expression of the CC expansion factors in porcine oocytes.