Tracheal relaxation of five Ivorian anti-asthmatic plants: Role of epithelium and K+ channels in the effect of the aqueous-alcoholic extract of Dichrostachys cinerea root bark

Leaves of Boerhavia diffusa (Nyctaginaceae), Baphia nitida, Cassia occidentalis, Desmodium adscendens (Fabaceae), and root bark of Dichrostachys cinerea (Fabaceae) are used in Ivory Coast for the treatment of asthma. The aim of this study was to evaluate the potential airway relaxant activity of different extracts of these plants. Extracts of different polarities (H2O, EtOH/H2O, MeOH and CH2Cl2) were obtained from these five plants. Their ex vivo relaxant activity was tested in mice isolated trachea precontracted with carbachol (1μM). Cumulative concentrations of most extracts induced moderate to strong relaxation, the methanolic extracts being the most potent and the polar extracts the most active at the concentrations used, supporting the traditional use of these five plants as anti-asthmatic remedies. We further investigated the molecular and cellular mechanisms of the mouse trachea relaxant effect of the aqueous-alcoholic extract of Dichrostachys cinerea root bark, the most potent extract. Its effect was not modified in the presence of β-adrenoceptor antagonists (propranolol or ICI 118,551) or a PKA inhibitor (H89). By contrast, it was decreased after depolarization-induced precontraction (with 80mM KCl), in the presence of some K+ channels blockers [4-aminopyridine as voltage-dependent K+ (Kv) channel blocker and tetraethylammonium chloride as large conductance Ca2+-activated K+ (BKCa) channel blocker, but not with glibenclamide, an ATP-sensitive K+ (KATP) channel blocker] or after epithelium removal. The mouse tracheal relaxant effect of Dichrostachys cinerea EtOH/H2O extract was independent of β2-adrenoceptors activation and cAMP/PKA pathway, but dependent on epithelium and K+ channels, namely Kv and BKCa channels. Further investigation will be required to identify the component(s) responsible for this airways relaxant activity.