Role of nitric oxide in hepatic ischemia-reperfusion with endotoxemia

Reactive oxygen species such as nitric oxide (NO) and/or superoxide have been proposed as mediators in the pathogenesis of reperfusion injury and acute endotoxemia. The purpose of this study was to examine the role of NO in a model of hepatic ischemia-reperfusion with endotoxemia (I/R + LPS). Rats subjected to 30 min of partial hepatic ischemia followed by reperfusion and LPS (Salmonella enteritidis, 1 mg/kg, i.v.,) administration, exhibited a marked, time-dependent increase in plasma alanine aminotransferase (ALT) levels compared to sham controls. An abrupt increase in liver nitrite/nitrate levels was also observed in I/R + LPS rats in association with the increases in plasma ALT. Although liver NO production in I/R + LPS rats increased with time, exacerbation of liver damage was not evident. Administration of L-NAME decreased NO production in plasma and liver but did not affect the liver damage in rats subjected to I/R + LPS. Superoxide levels in livers from I/R + LPS rats increased by threefold after 90 min reperfusion as compared to sham controls but dropped to control levels after 4 hr. There was a significant increase in neutrophils in liver lobes subjected to ischemia-reperfusion and LPS compared to sham controls and to non-ischemic lobes which received LPS. The number of neutrophils in the liver increased further in rats given L-NAME. These results suggest that the progressive injury seen in livers of I/R + LPS rats was possibly due to NO interaction with superoxide forming another reactive oxygen species such as peroxynitrite. However, inhibition of NO synthesis did not ameliorate liver damage, possibly because of an increase in tissue accumulation of activated polymorphonuclear leukocytes (PMN). Lung NO production increased in I/R + LPS rats after 4 hr reperfusion compared to sham controls. Prior administration of L-NAME did not prevent a significant rise in pulmonary NO generation (P < 0.05 at 90 min and 4 hr, compared to sham controls). This unexpected rise of pulmonary NO in the L-NAME treated group of rats was associated with a tendency for increased PMN accumulation (based on myeloperoxidase data) and superoxide generation. The results suggest that endogenous NO protected against excessive neutrophil infiltration in the lung in this model of hepatic ischemia-reperfusion and endotoxemia, and the use of L-NAME, a nonselective NOS inhibitor, may aggravate lung injury.