Antispasmodic and bronchodilator activities of Taxodium mucronatum Ten leaf extract

The relaxant effects of the Taxodium mucronatum Ten leaf hexane extract on intestinal and tracheal smooth muscle were evaluated in vitro by testing spontaneous contractions of rabbit jejunum and agonist-induced contractions of guinea pig ileum and rat trachea. The extract produced a concentration-dependent relaxation of the spontaneous contractions of rabbit jejunum (EC50: 4.9 ± 0.5 µg/ml) that was equipotent to papaverine. Following incubation of guinea pig ileum with the extract, the concentration-response curves to acetylcholine, histamine, 5-hydroxytryptamine and Ca2+ were displaced to the right and the maximum response was significantly reduced. K+-induced contraction of the ileal tissue was completely abolished with 31.6 µg/ml of the extract. In rat tracheal rings, the extract inhibited both 1 µM carbachol (EC50: 33.9 ± 2.5 µg/ml) and 60 mM K+ (EC50: 20.6 ±1.1 µg/ml)-induced contractions. It also caused the concentration-response to Ca2+curves to shift to the right in a non-competitive manner. These results demonstrate a non-specific relaxant effect that could be mediated through inhibition of calcium influx via both voltage- and receptor-gated calcium channels. The relaxant activity induced by this extract provides a rational basis for the traditional use of T. mucronatum to treat disorders of the gastrointestinal and respiratory tracts.   Key words: Taxodium mucronatum, Cupresaceae, muscular relaxant, antispasmodic, bronchodilator.