Interleukin 1 beta markedly stimulates nitric oxide formation in the absence of other cytokines or lipopolysaccharide in primary cultured rat hepatocytes but not in Kupffer cells.

To investigate whether a single inflammatory cytokine could stimulate nitric oxide formation in the absence of other cytokines or lipopolysaccharide (LPS), NO was measured by the redox chemiluminescence method in primary cultured rat hepatocytes and in rat Kupffer cells. Interleukin (IL) 1 beta, but neither IL-6, tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), nor LPS stimulated NO formation in a dose-dependent manner and induced half-maximal effects at 30 pmol/L. Maximal stimulation was achieved at 12 to 16 hours after the addition of 1I nmol/L of IL-1 beta, and was 50- to 60-fold above basal levels in rat hepatocytes. The combined effect of these cytokines with LPS or IFN-gamma on NO formation was also examined. Neither LPS nor IFN-gamma affected the IL-1 beta-induced NO formation. TNF-alpha, however, stimulated IL-1 beta-induced NO formation, while IL-6 inhibited it, although independently these cytokines had no effect on NO formation. None of the cytokines tested stimulated NO formation in cultured rat Kupffer cells. In hepatocytes, the NO formation induced by IL-l beta was blocked by both the NO synthase (NOS) inhibitor NG-monomethyl-L-arginine (L-NMMA) and by IL-1 receptor antagonist (IL-1ra). Furthermore, IL-1 beta markedly increased NOS activity, and this increase in activity was accompanied by the expression of inducible NOS (iNOS) messenger RNA (mRNA). This study clearly demonstrated that IL-1 beta markedly stimulates NO formation in hepatocytes, in the absence of other cytokines or LPS.