Expression of hepatic vascular stress genes following ischemia/reperfusion and subsequent endotoxemia

Hepatic ischemia and reperfusion (I/R) predisposes the liver to secondary stresses such as endotoxemia, possibly via dysregulation of the hepatic microcirculation secondary to an imbalanced regulation of the vascular stress genes. In this study, the effect of hepatic I/R on the hepatic vasoregulatory gene expression in response to endotoxin was determined. Rats were subjected to 90 min of hepatic ischemia and 6 h of reperfusion. Lipopolysaccharide (LPS, 1 mg/kg) was injected intraperitoneally after reperfusion. Plasma and liver samples were obtained 6 h after reperfusion for serum aminotransferase assays and RT-PCR analysis of the mRNA for the genes of interest: endothelin-1 (ET-1), its receptors ET A and ET B, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), heme oxygenase-1 (HO-1), cyclooxygenase-2 (COX-2), and tumor necrosis factor-alpha (TNF-alpha). The activities of serum aminotransferases were significantly increased in the I/R group. This increase was markedly potentiated by LPS treatment. The ET-1 mRNA was increased by LPS alone, and this increase was significantly greater in both the I/R alone and I/R + LPS groups compared to the sham. There were no significant differences in ET A receptor mRNA levels among any of the experimental groups. ET B mRNA was increased by both LPS alone and I/R alone, with no significant difference between the I/R alone and I/R + LPS groups. The eNOS and HO-1 transcripts were increased by I/R alone and further increased by I/R + LPS. The iNOS mRNA levels were increased by I/R alone, but increased significantly more by both LPS alone and I/R + LPS compared to I/R alone. The TNF-alpha mRNA levels showed no change with I/R alone, but were increased by both LPS alone and I/R + LPS. The COX-2 expression was increased significantly by I/R alone and significantly more by I/R + LPS. Taken collectively, significantly greater induction of the vasodilator genes over the constriction forces was observed with I/R + LPS. These results may partly explain the increased susceptibility of ischemic livers to injury as a result of endotoxemia.