Biol. Pharm. Bull. 30(1) 145—149 (2007)

tion of smooth muscle through the action of the enteric nerve system. Clinically, pain caused by gastrointestinal spasms is generally treated with drugs that induce smooth muscle relaxation. Shakuyakukanzoto (Shaoyao-Gancao-tang, an aqueous extract of a mixture of Paeoniae Radix and Glycyrrhizae Radix) and Kanzoto (an aqueous extract of Glycyrrhizae Radix) have been used clinically to relieve gastrointestinal pain. Shakuyakukanzoto has also been shown to exert a relaxant effect on acetylcholine (ACh)-induced contraction in rabbit ileum. Maeda et al. have reported that Glycyrrhizae Radix (licorice) extract inhibits the ACh-induced contraction of guinea pig ileum, whereas Paeoniae Radix extract has no such effect. Recently, we have isolated glycycoumarin as a potent antispasmodic from an aqueous extract of licorice and clarified that its mechanism of action involves inhibition of phosphodiesterase 3. During attempts to isolate antispasmodics from an aqueous extract of licorice, we found that other constituents in addition to glycycoumarin were present. In the present study, we attempted to characterize an antispasmodic principle of licorice other than glycycoumarin. We isolated isoliquiritigenin and found that it exerted a relaxant effect against the actions of various types of stimulants with a potency similar to that of papaverine (a representative antispasmodic for smooth muscle) in mouse jejunum.