Melatonin Impact on In Vitro Development of Mouse Preantral Follicles and Oocyte Maturation

Introduction: In vitro environments expose developing oocytes to excess reactive oxygen species (ROS) which are not normally produced in vivo. Melatonin acts as an indirect antioxidant and is a powerful direct free radical scavenger and direct responses to melatonin in the gonads. This study aims to investigate the influence of different doses of melatonin on follicle development and oogenesis of in vitro cultured mouse ovarian follicles. Materials and Methods: Preantral follicles with diameters of 150–175 μm were mechanically isolated from 18–21 day-old NMRI mouse ovaries. Follicles were individually cultured in micro droplets of α-minimal essential medium (α-MEM) supplemented with 5% FBS, 100 mIU/ml rhFSH, 1% ITS, 100 IU/ml penicillin and 100 μg/ml streptomycin in conjunction with varying doses of melatonin (0, 1, 10, 100 nM and 100, 500 pM) for six days. On day six, in vitro ovulation was induced by the addition of hCG/rEGF to the culture medium and after 16 h the maturation state of the oocytes was assessed. Results: On day six of culture there was a significant (P<0.05) decrease in the number of surviving follicles in the groups that received 10, 100 nM and 500 pM melatonin compared to the other groups. After induction of in vitro ovulation, follicles in groups that received 1, 10, and 100 nM melatonin had higher ovulation rates (P<0.05) compared with the other groups. Oocyte maturation capacity was adversely influenced by five concentrations of melatonin and GV arrest was significantly higher compared to the control group (P< 0.01). Conclusions: Our data indicates that a dose of 100 pM melatonin has no toxic effects on follicular development and can be used to reduce oxidative stress in follicle culture systems.