The influence of endogenous nitric oxide, which is generated by stimulation with lipopolysaccharide, on the mitochondrial energization of rat hepatocytes was investigated in vitro and ex vivo. Using a fluorescence microscope equipped with a silicon intensifier target camera, we visualized fluorescence of rhodamine‐123, a mitochondrial energization–sensitive fluorescence probe, in individual hepatocytes and measured the fluorescence intensity with a digital imaging processor. Although addition of Kupffer cells or lipopolysaccharide in a range of 0.1 to 1.0 νg/ml caused no significant alteration in the fluorescence in hepatocytes, Kupffer cells plus 1.0 μg/ml lipopolysaccharide reduced fluorescence intensity in the cocultured hepatocytes. The alteration of rhodamine‐123 fluorescence in the hepatocytes induced by lipopolysaccharide‐activated Kupffer cells was significantly inhibited by the addition of NG‐monomethyl‐L‐arginine, a selective inhibitor of nitric oxide synthesis. The transportal infusion of lipopolysaccharide also decreased rhodamine‐123 fluorescence in perfused rat liver. The decrease was significantly enhanced in the pericentral regions. Autofluorescence of NADH was elicited by continuous infusion of lipopolysaccharide; this reaction was also enhanced in the pericentral regions. We showed the main site of uptake of infused lipopolysaccharide in the hepatic lobule to be in the periportal regions with fluorescein isothiocyanate–labeled lipopolysaccharide. Our results indicate that the inhibition of mitochondrial energization occurs mainly in pericentral regions, which are distant from the lipopolysaccharide uptake site. The continuous administration of NG‐monomethyl‐L‐arginine significantly attenuated the lipopolysaccharide‐induced decrease in rhodamine‐123 fluorescence and increase of the NADH contents of the hepatic lobule. These results suggest that nitric oxide mediates the lipopolysaccharide‐activated, Kupffer cell–induced inhibition of mitochondrial electron transport in hepatocytes. (HEPATOLOGY 1993;18:380–388).
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