Ginsenoside-induced relaxation of human bronchial smooth muscle via release of nitric oxide

1 Ginsenoside, an extract of Panax ginseng, is an essential constituent of anti-asthmatic Chinese herbal medicine. To elucidate whether ginsenoside af fects airway smooth muscle tone and, if so, what the mechanism of action is , we studied relaxant responses of human bronchial strips under isometric c ondition in vitro, and directly measured the release of nitric oxide (NO) b y an amperometric sensor for this molecule. 2 Addition of ginsenoside relaxed the tissues precontracted with acetylchol ine in a dose-dependent manner, the maximal relaxation and the ginsenoside concentration required to produce 50% relaxation being 67+/-8% and 210+/-29 mu g ml(-1), respectively. 3 The relaxant responses to ginsenoside were inhibited by N-G-nitro-L-argin ine methylester (L-NAME) and removal of the epithelium, but not by NG-nitro -D-arginine methylester (D-NAME) or tetrodotoxin. This inhibitory effect of L-NAME was reversed by L-arginine but not by D-arginine. 4 Addition of ginsenoside to the medium containing bronchial tissues dose-d ependently increased NO-selective electrical current, and this effect was g reatly attenuated by the epithelial removal or Ca2+-free medium. 5 Ginsenoside also increased tissue cyclic GMP contents, an effect that was abolished in the presence of L-NAME. 6 It is concluded that ginsenoside induces relaxation of human bronchial sm ooth muscle via stimulation of NO generation predominantly from airway epit helium and cyclic GMP synthesis. This action might account for the anti-ast hmatic effect of Panax ginseng.