The nitric oxide-producing activities of Scutellaria baicalensis

Scutellaria baicalensis (SB) has antibacterial and antiviral activities. Nitric oxide (NO) as a potent macrophage-derived effector molecule against a variety of bacteria, viruses and tumors has received increasing attention. The objective of this study was to determine the effect of SE on the production of NO. Stimulation of mouse peritoneal macrophages with SE after the treatment of recombinant interferon-gamma (rIFN-gamma) resulted in the increased NO production. SE had no effect on NO production by itself. When SE was used in combination with rIFN-gamma, there was a marked cooperative induction of NO production in a dose-dependent manner. The optimal effect of SE on NO production was shown 6 h after treatment with rIFN-gamma. NO production by SE was inhibited by N-G-monomethyl-L-arginine. The increased production of NO from rIFN-gamma plus SE-stimulated cells was decreased by the treatment of protein kinase C inhibitor such as staurosporin. In addition, synergy between rIFN-gamma and SE was mainly dependent on SE-induced tumor necrosis factor-alpha (TNF-alpha) secretion. All the preparations of SE were endotoxin free. These results suggest that the capacity of SE to increase NO production from rIFN-gamma-primed mouse peritoneal macrophages is the result of SE-induced TNF-gamma secretion. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.