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 in dicators of oxidative stress in the tissue. Hydroperoxide-initiated ch emiluminescence and the activity of antioxidant enzymes (catalase, sup eroxide dismutase and glutathione peroxidase) were also measured to ev aluate antioxidant defenses and serum activity of lactate dehydrogenas e and aspartate aminotransferase. Mitochondrial morphology and mitocho ndrial respiratory control ratio were measured as indicators of cell a nd mitochondrial damage. Xanthine dehydrogenase and xanthine oxidase a ctivities were determined as a possible source of oxyradicals. No sign ificant changes were observed after 1 0 or 30 min of vena cava occlusi on in any of the measured parameters. In contrast, 10 min of occlusion followed by 10 min of reperfusion increased chemiluminescence (from 1 8 +/- 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 swellin g and decreased mitochondrial respiratory control (from 5.6 +/- 0.3 to 2.6 +/- 0.1). The activity of the antioxidant enzymes and xanthine ox idase 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 mitoch ondrial morphology or respiratory control (2.4 +/- 0.1) in isolated mi tochondria. A parallel decrease in the activity of cytosolic (36%) and mitochondrial (57%) superoxide dismutase, catalase (34%) and glutathi one peroxidase (34%) was also observed without any change in xanthine oxidase activity. Chain-breaker antioxidants were also diminished as i ndicated by an increase in the hydroperoxide-initiated chemiluminescen ce (40%). The results indicate the occurrence of an oxidative stress i n association with a sequence of 10 or 30 min of occlusion followed by 10 min of reperfusion. The unchanged activity of xanthine oxidase, th e modifications in mitochondrial morphology, the decrease in mitochond rial respiratory control and the relatively high inactivation of the m itochondrial superoxide dismutase indicate that the mitochondria are t he 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.