Objective To investigate the inhibitory mechanism of emodin on lipopolysaccharide(LPS)-induced nitric oxide(NO)generation in rat peritoneal macrophages.Methods NO production and iNOS expression were measured through nitrite assay and Western blotting assay,respectively.NF-kB activity and nuclei P65 expression were estimated by dual-luciferase and Western blotting assay,respectively.Intracellular free Ca2+([Ca2+]i)was detected using the ratiometric fluorescent calcium indicator dye,Fura-2,and a microspectrofluorometer.PLC-γphosporylation was analyzed by Western blotting assay.Results First,emodin was found playing active roles in suppressing LPS-induced NF-kB activation in rat peritoneal macrophages.Second,emodin down-regulated transient[Ca2*]i and could increase in NF-kB upstream signal.Finally,emodin suppressed phosphorylation of PLC-γ by LPS stimulation in the upstream of[Ca2+]i.Conclusion Suppression of PLC-γ phosphorylation is involved in emodin inhibiting NO generation by LPS stimulation in rat peritoneal macrophages.