NORMOTHERMIC LIVER ISCHEMIA IN RATS - XANTHINE-OXIDASE IS NOT THE MAIN SOURCE OF OXYGEN-FREE RADICALS

We studied the effect of allopurinol (ALL) on the activity of xanthine dehydrogenase (XDH), xanthine oxidase (XOX), superoxide dismutase (SO D), and catalase (CAT) in rat liver during ischemia followed by 60 min of reperfusion. We induced 60-min ischemia in the median and left lob es by clamping the hepatic artery and portal branches. The percentage XOX relative to total oxidase activity increased significantly in the control group, from 10% during the stabilization period to 18% after 6 0 min of reperfusion. The XDH activity decreased during reperfusion. A ctivity of both XDH and XOX was almost completely blocked by ALL. The activity of SOD and CAT did not differ significantly between the ALL g roup and controls after 60 min of reperfusion. ALL treatment did not a ffect liver injury parameters, as concentrations of lactate dehydrogen ase (LDH) and alanine transferase (ALT) increased in plasma after isch emia, both in controls and in the ALL-treated group. We concluded that ischemia promotes conversion of XDH to XOX during reperfusion. XOX ma y not be the main source of free radical production, since intracellul ar scavengers (SOD and CAT) did not differ significantly between contr ols and the ALL-treated group, despite the fact that ALL blocked XOX a ctivity completely.