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, N O might react instead with hemoglobin. The aim of this study was to co mpare 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 i nduced in vivo by preadministration of killed Corynebacterium parvum; 7 days later, rats received endotoxin and were killed after 6 hours, T hird, mitochondria were exposed to sodium nitroprusside in vitro, wash ed, 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 fo rmation of hemoglobin-NO complexes in blood, no iron-nitrosyl complex was detected in hepatic mitochondria, and hepatic mitochondrial functi on was not impaired. In the third model, mitochondria lost preformed i ron-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 mitocho ndrial function.