Antispasmodic activity of licochalcone A, a species‐specific ingredient of Glycyrrhiza inflata roots

Licochalcone A, a species-specific and characteristic retrochalcone ingredient of Glycyrrhiza inflata root, has been shown to possess multiple bioactive properties. However, its muscle relaxant activity has not been reported previously. Licochalcone A showed a concentration-dependent relaxant effect on the contraction induced by carbachol (50% effective concentration (EC50) = 5.64 ± 1.61 μM), KCl (EC50 5.12 ± 1.68 μM), BaCl 2 (EC50 1.97 ± 0.48 μM) and A23187 (EC50 2.63 ± 2.05 μM). Pretreatment with licochalcone A enhanced the relaxant effect of forskolin, an adenylyl cyclase activator, on the contraction in a similar manner to 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase (PDE) inhibitor. Furthermore, the IC50 (22.1 ± 10.9 μM) of licochalcone A against cAMP PDE was similar to that of IBMX (26.2 ± 7.4 μM). These results indicated that licochalcone A may have been responsible for the relaxant activity of G. inflata root and acted through the inhibition of cAMP PDE.