Reactive oxygen species in ovarian physiology.

Cells living under aerobic conditions always face oxygen paradox. Oxygen is necessary for cells to maintain their lives. However, reactive oxygen species such as superoxide radical ( ), hydroxyl radical (OH-) and hydrogen peroxide (H2O2) are generated from oxygen and damage cells. Oxidative stress occurs as a consequence of excessive production of reactive oxygen species and impaired antioxidant defense systems. Antioxidant enzymes include: superoxide dismutase (SOD), which is a specific enzyme to scavenge superoxide radicals; copper-zinc SOD, located in the cytosol; and manganese SOD, located in the mitochondria. Both types of SOD belong to the first enzymatic step to scavenge superoxide radicals. It has been reported that a number of local factors such as cytokines, growth factors and eicosanoids are involved in the regulation of ovarian function, in addition to gonadotropins and ovarian steroid hormones. Since reactive oxygen species are generated and SOD is expressed in the ovary, there is a possibility that reactive oxygen species and SOD work as local regulators of ovarian function. The present review reports that reactive oxygen species and their scavenging systems play important roles in several processes of reproductive physiology, including follicular development, oocyte maturation, ovulation, corpus luteum function and follicular atresia. (Reprod Med Biol 2005; 4: 31- 45).