OXIDATIVE STRESS PRODUCED BY SUPRAHEPATIC OCCLUSION AND REPERFUSION

In this article the spontaneous chemiluminescence and the steady-state concentration of hydrogen peroxide were determined in rat liver as indicators of oxidative stress in the tissue. Hydroperoxide-initiated chemiluminescence and the activity of antioxidant enzymes (catalase, superoxide dismutase and glutathione peroxidase) were also measured to evaluate antioxidant defenses and serum activity of lactate dehydrogenase and aspartate aminotransferase. Mitochondrial morphology and mitochondrial respiratory control ratio were measured as indicators of cell and mitochondrial damage. Xanthine dehydrogenase and xanthine oxidase activities were determined as a possible source of oxyradicals. No significant changes were observed after 1 0 or 30 min of vena cava occlusion in any of the measured parameters. In contrast, 10 min of occlusion followed by 10 min of reperfusion increased chemiluminescence (from 18 +/- 3 to 32 +/5 cps/cm2), hydrogen peroxide (from 0.10 +/- 0.01 to 0.17 +/- 0.01 mumol/L), lactate dehydrogenase (from 80 +/- 2 to 330 +/- 30 U/L), and aspartate aminotransferase (from 42 +/- 2 to 100 +/- 10 U/L). Liver reperfusion was also associated with mitochondrial swelling and decreased mitochondrial respiratory control (from 5.6 +/- 0.3 to 2.6 +/- 0.1). The activity of the antioxidant enzymes and xanthine oxidase was instead without change. After 30 min of vena cava occlusion and 10 min of reperfusion a more marked increase in chemiluminescence (37 +/- 5 cps/cm2), hydrogen peroxide (0.30 +/- 0.01 mumol/L), lactate dehydrogenase (730 +/- 10 U/L) and aspartate aminotransferase (140 +/- 10 U/L) was observed. No further changes were found in either mitochondrial morphology or respiratory control (2.4 +/- 0.1) in isolated mitochondria. A parallel decrease in the activity of cytosolic (36%) and mitochondrial (57%) superoxide dismutase, catalase (34%) and glutathione peroxidase (34%) was also observed without any change in xanthine oxidase activity. Chain-breaker antioxidants were also diminished as indicated by an increase in the hydroperoxide-initiated chemiluminescence (40%). The results indicate the occurrence of an oxidative stress in association with a sequence of 10 or 30 min of occlusion followed by 10 min of reperfusion. The unchanged activity of xanthine oxidase, the modifications in mitochondrial morphology, the decrease in mitochondrial respiratory control and the relatively high inactivation of the mitochondrial superoxide dismutase indicate that the mitochondria are the main source of oxyradicals during reperfusion. An increased rate of superoxide radical and hydrogen peroxide generation by mitochondria, associated with a decreased activity of antioxidant enzymes, would be the major causes of oxidative stress and the related cell damage.