The nitric oxide-producing properties of Ulmi radicis cortex extract

We investigated the effect of Ulmi radicis cortex extract (UrCE) on the pro duction of nitric oxide (NO). Stimulation of mouse peritoneal macrophages w ith UrCE after the treatment of recombinant interferon-gamma (rIFN-gamma) r esulted in the increased NO synthesis. UrCE had no effect on NO synthesis b y itself. When UrCE was used in combination with rIFN-gamma, there was a ma rked cooperative induction of NO synthesis in a dose-dependent manner. The optimal effect of UrCE on NO synthesis was shown 6 h after treatment with r IFN-gamma. NO production was inhibited by N-G-monomethyl-L-arginine. The in creased production of NO from rIFN-gamma plus UrCE-stimulated cells was dec reased by the treatment of protein kinase C inhibitor such as staurosporin. In addition, synergy between rIFN-gamma and UrCE was mainly dependent on U rCE-induced tumor necrosis factor-alpha (TNF-alpha) secretion. All the prep arations of UrCE were endotoxin free. These results suggest that the capaci ty of UrCE to increase NO production from rIFN-gamma-primed mouse peritonea l macrophages is the result of UrCE-induced TNF-alpha secretion.