Inhibitory Effect of Xanthomicrol and 3α-Angeloyloxy-2α-hydroxy-13,14Z-dehydrocativic Acid from Brickellia paniculata on the Contractility of Guinea-Pig Ileum

Abstract

Chemical fractionation of Brickellia paniculata methanolic extract by monitoring its inhibitory effect on K⁺-induced contraction in guinea-pig ileum in vitro led to the isolation of 5,4′-dihydroxy-6,7,8-trimethoxyflavone (xanthomicrol) and the labdane-diterpene 3α-angeloyloxy-2α-hydroxy-13,14Z-dehydrocativic acid (AAHDD). Both compounds inhibited the tonic contraction the effect being highly potent when a mixture in a proportion of 3 : 1 (xanthomicrol/AAHDD) was assayed. The phasic component of the contractile response with K⁺ was also reduced by the compounds. Xanthomicrol depressed the spasms induced with ACh, Hist, and BaCl₂ and its effect on Ca²⁺ concentration-response curve showed a type of non-surmountable calcium blocking action; unlike the flavonoid, AAHDD produced a parallel rightward shift of the concentration-response curve to calcium, suggesting a competitive antagonism with an estimated pA₂ of 4.66. Obtained results support, in part, the popular use of B. paniculata as a spasmolytic remedy.