To better understand how gut-derived endotoxins influence alcohol-induced liver injury and the expression of inflammatory cytokines a new animal model was developed. After 2 weeks on a modified ethanol-containing liquid diet, some rats also were infused with endotoxin via osmotic minipumps for 4 additional weeks. Ethanol diet alone increased plasma endotoxin threefold to 9.3 pg/mL. Endotoxin infusion increased the levels to 388 and 513 pg/mL in controls and ethanol-fed animals, respectively. Panlobular macrovesicular and microvesicular steatosis and inflammatory foci were observed in livers from both ethanol- and ethanol-endotoxin-treated animals, but there was no significant potentiation by endotoxin. Only minor changes, mainly polymorphonuclear infiltration, were seen in animals treated with endotoxin alone although the messenger RNA (mRNA) expression of both proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta) and anti-inflammatory cytokines IL-4 and IL-10 were markedly increased, as shown by competitive polymerase chain reaction (PCR) analysis using cyclophilin as standard. The effect of endotoxin infusion on cytokine mRNA expression in ethanol-fed animals was not significantly different. Expression of transforming growth factor beta1 (TGF-beta1) mRNA was increased twofold by ethanol, eightfold by endotoxin, but only threefold by ethanol-endotoxin treatment. The mRNA expression of lipopolysaccharide binding protein (LBP) and CD14 endotoxin receptor was not significantly increased by chronic endotoxin treatment, contrasting with the marked elevation observed after acute endotoxin challenge. These results suggest that the tolerance observed despite sustained hepatic expression of proinflammatory cytokines is counteracted by the anti-inflammatory cytokines and by down-regulation of CD14 and LBP. Furthermore, a similar adaptation may occur in alcoholics with continuous endotoxemia.