Effect of chronic ethanol feeding on nitric oxide synthesis by rat Kupffer cells

Kupffer cells contribute to the Important role of the liver defense mechanism through nitric oxide (NO) production. In this study, the effect of chronic ethanol administration on the ability of Kupffer cells to synthesize and release NO was investigated after stimulation with lipopolysaccharide (LPS). Male Wistar rats were chronically fed ethanol for 8 weeks according to the method described by DeCarti and Lieber et al. (J Nutr. 91:331-336, 1967). Kupffer cells were isolated and cultured with LPS (1 μg/ml) for 24 hr. The levels of nitrite and nitrate, metabolites of NO, were determined in the culture medium. NO synthase (NOS) activity in Kupffer cells was determined by the method that measures conversion of [¹⁴C]arginine into [¹⁴C]citrulline. In control rats, a significant increase of nitrite and nitrate levels in culture medium was observed after LPS treatment. The magnitude of this increase was significantly smaller in chronic ethanol-fed rats. When the activity of NOS was determined, inducible NOS (iNOS) activity was higher than that of constitutive NOS, and LPS administration produced a significant elevation of iNOS activity in both control and chronic ethanol-fed rats. However, the elevation of iNOS activity by LPS stimulation was diminished by chronic ethanol administration. Distribution of iNOS in Kupffer cells as determined by an immunofluorescence method using a laser scanning confocal image system showed a lower expression of iNOS in chronic ethanol-fed rats even in the presence of LPS. These results demonstrate that the excessive production of NO by increased iNOS activity in Kupffer cells is diminished by chronic ethanol administration.