Nitric oxide inhibits neonatal hepatocyte oxidative metabolism

Background/Porpose: Liver function is frequently impaired in neonates with sepsis. Nitric oxide (NO) is thought to be a mediator of organ dysfunction and liver oxidative metabolism during sepsis. The authors developed an in v itro model to investigate the effect of NO and the combined effect of NO pl us H2O2 on neonatal hepatocyte oxidative metabolism. Methods: Hepatocytes were isolated from neonatal rats. Oxygen consumption w as measured polarographically. In Study A, cells were exposed to S-Nitroso- N-acetylpenicillamine (SNAP), an NO donor, at various concentrations. In st udy B, myxothiazol and oligomycin, inhibitors of mitochondrial respiration, were added to investigate the site of action of NO. In study C, hepatocyte s were incubated in the presence of both SNAP (300 mu mol/L) and H2O2 (1.5 mmol/L). In study D, morphological alterations induced by NO and NO plus H2 O2 were investigated by hepatocyte electron microscopy. Results: In study A, SNAP caused a dose-dependent decrease in oxygen consum ption. A significant inhibition was reached at 300 mu mol/L SNAP. In study B, the lack of further inhibition when SNAP was given together with myxothi azol indicates that NO acts intramitochondrially. Similarly, no further inh ibition occurred when the NO donor was given together with oligomycin, sugg esting that the effect of NO is mainly at the level of ATP synthase. In stu dy C, concomitant addition of 300 mu mol/L SNAP and 1.5 mmol/L H2O2 to hepa tocytes caused further inhibition of oxygen consumption compared with eithe r SNAP or H2O2 alone. In study D, mild alterations in hepatocyte morphology were noted in the presence of SNAP or SNAP plus H2O2. Conclusions: In neonatal hepatocytes, NO significantly inhibits mitochondri al oxygen consumption, possibly at the level of ATP synthase. The effect of NO is additive to that of H2O2 Morphological findings were consistent with these biochemical effects and suggest that NO and H2O2 are important media tors of liver damage during sepsis. Copyright (C) 2000 by W.B. Saunders Com pany.