Xanthine oxidase and dehydrogenase activities in rat ovarian tissues

The production of reactive oxygen species in the ovary is rapidly inducible, but the nature of the generator is unknown. One possibility is xanthine oxidase (XO), an enzyme that produces superoxide in the presence of hypoxanthine (or xanthine) and oxygen. The objective of the present studies was to measure levels of XO in follicular and luteal tissue to determine whether XO may be a source of reactive oxygen species in the rat ovary. Ovarian levels of XO were about one-fifth of that seen in the liver and adrenal, and XO levels were about one-third of xanthine dehydrogenase (XDH). Preovulatory ovarian levels of XO activity were unchanged after induction of ovulation with gonadotropin and in follicles incubated with gonadotropin. Luteal XO activity was not changed during natural or prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis. Allopurinol, an inhibitor of XO, did not inhibit ovulation or PGF2 alpha-induced luteal regression. Finally, neither catalase and superoxide dismutase nor oxypurinol altered luteal cell function in the presence of hypoxanthine. Thus, while XO is present in the ovary, it does not appear that it is a major source of reactive oxygen species in this organ.