Melatonin improves the in vitro growth of bovine oocytes collected from early antral follicles by maintaining oocyte-cumulus cell communication

PurposeIn vitro, oocyte development is susceptible to oxidative stress, which leads to endoplasmic reticulum (ER) stress. This study investigated whether the antioxidant melatonin attenuates ER stress and maintains oocyte-cumulus cell communication during the in vitro growth (IVG) of bovine oocytes.MethodsOocyte-granulosa cell complexes (OGCs) were harvested from slaughterhouse-derived ovaries and grown in vitro for 5 d at 38.5 degrees C in 5% CO2 humidified air. Melatonin (10-7, 10-9, or 10-11 M) was added to the culture medium.ResultsOocyte diameter increased on day 5 from its initial value in all groups. The antrum formation rate was significantly higher in the 10-9 M melatonin-treated group than in the control. The melatonin-treated group showed reduced oxidative stress and increased gap junction communication compared with the control. ER stress-related genes in OGCs were significantly downregulated in the 10-9 M melatonin-treated group compared with those in the control. No significant changes were found in subsequent maturation among groups; however, 10-9 M melatonin treatment during IVG and IVM increased the maturation rate compared with that in the control.ConclusionsMelatonin reduces oxidative stress, which attenuates ER stress in OGCs during IVG of bovine oocytes and may improve IVG efficiency in assisted reproductive technology.