Nitric oxide and ovarian function

Nitric oxide (NO) is synthesized by three NO synthases, designated as NOS‐1, NOS‐2, and NOS‐3, with distinct features and localization. Nitric oxide and the reactive oxygen species generated from NO react with a wide variety of biomolecules such as DNA, transcription factors, enzymes, cytokines, and membrane receptors in NO synthesized cells and nearby cells to mediate a variety of biological functions. Nitric oxide synthase‐2 and NOS‐3 are expressed in the ovary during folliculogenesis and luteinization. Nitric oxide functions as an important modulator for folliculogenesis and atresia, steroidogenesis, prostaglandin biosynthesis, ovulation, luteolysis, and oocyte maturation. Nitric oxide synthase‐3 is also localized in the porcine oocytes of the primordial follicles as well as in large follicles. It has been proved that NO is involved in intracellular signaling for oocyte growth and maturation at the pre‐ovulatory stage.