Oxygen-derived free radicals might play a role in the injury produced by reperfusion of ischemic organs. Since the generation of reactive oxygen species results in an increased formation of glutathione disulfide, we have attempted to document an oxidant stress during reperfusion of ischemic liver by following the hepatic production of glutathione disulfide in vivo and in the perfused rat liver. Following partial hepatic ischemia of 120 min duration, the plasma concentration of glutathione disulfide gradually increased from 0.8 +/- 0.1 to 9.1 +/- 1.6 microM (mean +/- S.E., n = 6) after 1 hr of reperfusion. The plasma concentration of reduced glutathione increased only 2-fold from 21.4 +/- 2.4 to 38.1 +/- 3.4 microM. The rise in plasma glutathione disulfide was higher with increasing duration of ischemia from 30 to 120 min and was associated with a gradual increase in hepatic glutathione disulfide. The hepatic origin of glutathione disulfide was documented in the perfused rat liver where the release of glutathione disulfide increased gradually during reperfusion following 90 min of warm ischemia from 1.0 +/- 0.1 to 2.6 +/- 0.5 nmole per min per gm liver at 30 min after onset of reperfusion. The administration of allopurinol, an inhibitor of xanthine oxidase, did not decrease the release of glutathione disulfide (29.9 +/- 3.8 nmoles per gm in controls vs. 44.7 +/- 10.0 nmoles per gm in 30 min with allopurinol) and ALT (3.3 +/- 1.4 units per gm in controls vs. 2.6 +/- 0.8 units per gm in 30 min with allopurinol). Our studies document an oxidant stress associated with reperfusion of ischemic liver.(ABSTRACT TRUNCATED AT 250 WORDS)