Endotoxin and TNF alpha directly stimulate nitric oxide formation in cultured rat hepatocytes from chronically endotoxemic rats

We examined the effects of endotoxin on nitric oxide formation in isolated rat hepatocytes in primary culture. Endotoxin was administered either in vivo, by continuous infusion for 30 or 3 h, or in vitro, on cultured cells. The spontaneous production of nitrites in hepatocytes from in vivo ET-infused rats was lower than equivalent saline controls in the absence of added stimuli. However in vitro addition of endotoxin in culture to hepatocytes from 30 h ET-infused rats greatly enhanced production relative to saline controls. This effect was mimicked by TNF alpha, and activators of protein kinase C (PMA and Ca2+ ionophore A23187). The effects of ET were blocked by NMMA, dexamethasone and protein synthesis inhibitors Actinomycin D and cycloheximide. No in vitro effect of ET was observed in the 3 h infusion model. The results show that chronic exposure to sub-lethal levels of ET primes liver parenchymal cells for the production of nitric oxide, when exposed in vitro to ET or TNF alpha.