Potent Airway Smooth Muscle Relaxant Effect of Cynatratoside B, a Steroidal Glycoside Isolated from <i>Cynanchum stauntonii</i>

The dried roots of <i>Cynanchum stauntonii</i> in having cough-relieving efficacy are commonly included in traditional antitussive formulas. The active components in a <i>C. stauntonii</i> root extract responsible for airway relaxation were isolated using an ex vivo bioassay-guided fractionation method, in which subfractions were evaluated for their inhibitory effects on the contraction of isolated rat tracheal rings by isometric tension measurements. A steroidal glycoside, cynatratoside B (<b>1</b>), identified by LC-MS and NMR spectroscopic analysis, was shown to have potent inhibition on acetylcholine- and carbachol-induced tracheal contractions. The present data provide scientific evidence to support the traditional use of <i>C. stauntonii</i> as an antitussive herbal medicine