excess calcium influx from membranes pump failure activates an intracellular protease, which convert xanthine dehydrogenase to XO .when oxygen is reintroduce upon reperfusion the enzyme XO converts hypoxanthine to xanthine and the superoxide radical.further reactions ultimately lead t o production of hydrogen peroxide and the highly reactive hydroxyl radical. Although considerable emphasis has been placed on the importance of the XO pathway in I-R, the effect of allopurinol (a XO inhibitor) in various reperfusion models have been mixed (22,23) this has led to the study of additional sources of oxyadicals.