Insights into mechanisms underlying the gut and airways modulatory effects of Swertia chirata

Swertia chirata is used in folk medicine for the treatment of constipation, colic, diarrhea, and asthma. This study was carried out in order to provide a pharmacological basis for its medicinal use in gastrointestinal and respiratory disorders. Crude extract of Swertia chirata (Sc.Cr) and its fractions were studied using rabbit isolated tissue preparations. In jejunum, Sc.Cr, which tested positive for alkaloids, flavonoids, saponins, tannins, and terpenes, caused stimulation at concentrations of 0.01-1.0 mg/mL, followed by a relaxant effect at higher concentrations. In the presence of atropine, the contractile effect was blocked and only relaxation occurred. Sc.Cr inhibited high K ⁺ (80 mM)-induced contractions at 0.01-10 mg/mL and shifted Ca ²⁺ concentration-response curves to the right, similar to that caused by verapamil. In trachea, Sc.Cr relaxed the carbachol (1 μM) and high K ⁺-induced contractions, in a pattern similar to that of verapamil. Bioassay directed fractionation revealed the separation of spasmogenic and spasmolytic components in aqueous and organic fractions, respectively. The chloroform fraction exhibited a concentration-dependent (0.1-3.0 mg/mL) bronchodilator effect. These results indicate that Swertia chirata exhibits gut excitatory and inhibitory effects, mediated through cholinergic and Ca ²⁺ antagonist mechanisms, respectively, as well as bronchodilatation, via Ca ²⁺ channel blockade. Thus, this study provides a sound mechanistic background for the therapeutic application of Swertia chirata in gut motility disorders, such as constipation, colic, and diarrhea, and airways hyperactivity disease, such as asthma.