Cell-generated nitric oxide inactivates rat hepatocyte mitochondria in vitro but reacts with hemoglobin in vivo

Background & Aims: Nitric oxide forms inactive iron-nitrosyl complexes within hepatic mitochondria in vitro, However, when formed in vivo, NO might react instead with hemoglobin. The aim of this study was to compare the effects of cell-derived NO on rat hepatocyte mitochondria in vitro and in vivo. Methods: First, hepatocytes were cultured in vitro for 24 hours under a porous membrane supporting macrophages that were stimulated by endotoxin. Second, hepatic macrophage hyperplasia was induced in vivo by preadministration of killed Corynebacterium parvum; 7 days later, rats received endotoxin and were killed after 6 hours, Third, mitochondria were exposed to sodium nitroprusside in vitro, washed, mixed with blood, and recovered. Results: Iron-nitrosyl complexes and hepatocyte mitochondrial dysfunction were observed in the in vitro model and prevented by an NO synthase inhibitor. In the in vivo model, however, despite a 130-fold increase in plasma nitrate levels and formation of hemoglobin-NO complexes in blood, no iron-nitrosyl complex was detected in hepatic mitochondria, and hepatic mitochondrial function was not impaired. In the third model, mitochondria lost preformed iron-nitrosyl complexes when exposed to blood. Conclusions: Although NO reacts with hepatocyte mitochondria in vitro, in vivo it reacts with sinusoidal hemoglobin without detectable impairment of hepatic mitochondrial function.