Steatosis is a major risk factor for complications after liver surgery. Since neutrophil cytotoxicity is critical for ischemia-reperfusion injury in normal livers, the aim of the present study was to evaluate whether an exaggerated inflammatory response could cause the increased injury in steatotic livers. In C57Bl/6 mice, 60 min of warm hepatic ischemia triggered a gradual increase in hepatic neutrophil accumulation during reperfusion with peak levels of 100-fold over baseline at 12 h of reperfusion. Neutrophil extravasation and a specific neutrophil-induced oxidant stress (immunostaining for hypochlorous acid-modified epitopes) started at 6 h of reperfusion and peaked at 12-24 h. Ob/ob mice, which had a severe macrovesicular steatosis, suffered significantly higher injury (alanine transaminase activity: 18,000 +/- 2,100 U/l; 65% necrosis) compared with lean littermates (alanine transaminase activity: 4,900 +/- 720 U/l; 24% necrosis) at 6 h of reperfusion. However, 62% fewer neutrophils accumulated in steatotic livers. This correlated with an attenuated increase in mRNA levels of several proinflammatory genes in ob/ob mice during reperfusion. In contrast, sham-operated ob/ob mice had a 50% reduction in liver blood flow and 35% fewer functional sinusoids compared with lean littermates. These deficiencies in liver blood flow and the microcirculation were further aggravated only in ob/ob mice during reperfusion. The attenuated inflammatory response and reduced neutrophil-induced oxidant stress observed in steatotic livers during reperfusion cannot be responsible for the dramatically increased injury in ob/ob mice. In contrast, the aggravated injury appears to be mediated by ischemic necrosis due to massive impairment of blood and oxygen supply in the steatotic livers.