Oocyte mitochondrial bioenergy potential and oxidative stress: within-/between-subject, in vivo versus in vitro maturation, and age-related variations in a sheep model

Objective: To analyze within-/between-subject, in vivo versus in vitro maturation (IVM), and age-related variations of mitochondrial (mt) bioenergy potential and oxidative status of metaphase II (MII) oocytes recovered from hormonally stimulated sheep. Design: Prospective study. Setting: Academic basic research laboratory. Subject(s): Ten adult ewes. Intervention(s): Estrus synchronization, controlled ovarian hyperstimulation (COH), ovariohysterectomy; follicular and oviductal oocyte retrieval; IVM of follicular oocytes. Main Outcome Measure(s): Mean +/- SD, within-subject (CVw) and between-subject (CVb) variation coefficients of mt activity, intracellular reactive oxygen species (ROS) levels, and mt/ROS colocalization in sheep oocytes from young and aged donors and matured in vivo (in vivo MIIs) or in vitro (IVM MIIs). Result(s): Within- and between-subject, in vivo versus IVM, and age-related variations of mt activity were observed in MII oocytes from hormonally stimulated donor sheep. ROS levels increased significantly in oocytes from aged donors. Mt-ROS colocalization was consistently higher in in vivo MIIs compared with IVM MIIs. Oviductal energy/antioxidant ability is influenced by COH. Conclusion(s): Oocyte energy/oxidative status is affected by within-/between-subject, in vivo versus IVM, and age-related variations. Mt/ROS colocalization is a reliable marker of in vivo MII oocytes. (Fertil Steril (R) 2012; 97: 720-8. (c) 2012 by American Society for Reproductive Medicine.)