Regulation of inducible nitric oxide synthase and nitric oxide during hepatic injury and fibrogenesis.

Nitric oxide (NO) production via inducible NO synthase (iNOS) is prominent in the liver after stimulation with cytokines and/or lipopolysaccharide. The aim of this study was to investigate the production of NO via iNOS in specific liver cell populations during toxin-mediated and obstructive hepatic injury and fibrogenesis. After a single dose of carbon tetrachloride, iNOS mRNA and nitrite (a metabolic product of NO) were detected only in Kupffer cells. They were not detectable in any cell type after recurrent administration of carbon tetrachloride, including in animals with far advanced cirrhosis (i.e., portal hypertension and/or ascites). After bile duct ligation, a mechanistically different form of liver injury and fibrogenesis, iNOS mRNA and nitrite were identified in all nonparenchymal cells but not in hepatocytes. Twenty-four hours after bile duct ligation, iNOS mRNA and NO production were greatest in Kupffer cells, but after prolonged bile duct ligation, iNOS was found predominantly in sinusoidal endothelial cells. These data indicate that iNOS expression varies temporally and spatially in the liver after injury and also varies with the type of insult.