Antidiarrheal activity of methanol extract of Sophora tonkinensis in mice and spasmolytic effect on smooth muscle contraction of isolated jejunum in rabbits

Context: In China, the herb Sophora tonkinensis Gagnep. (Fabaceae, ST) (Committee of National Pharmacopeia. 2015) exhibits anti-inflammatory, antitumor, and Antiviral effects. However, to date, there have been few studies on its gastrointestinal effect. Objective: The gastrointestinal effect of the methanol extract of ST rhizome (STR) was evaluated. Materials and methods: Study was conducted from February to December 2018. In vivo, antidiarrheal activity of STR (125, 250 and 500 mg/kg; orally) in castor oil-induced diarrheal mice was studied. In vitro, the effects of STR (0.01-10 mg/mL) on the isolated tissue preparations of rabbit jejunum were also investigated, the rabbit jejunum stripes were pre-contracted with Ach (10^-5 M), K⁺ (60 mM) and tested in the presence of STR, the possible spasmolytic effect was analyzed in the pretreatment of the jejunum preparations with STR or verapamil in CA²⁺-free high-K⁺ (60 mM) solution containing EDTA. Results: STR (125, 250 and 500 mg/kg) exhibited antidiarrheal activity. STR (0.01-10 mg/mL) completely relaxed spontaneously contracting, Ach (10^-5 M) and high K⁺ (60 mM) induced contracted jejunum with an EC₅₀ value of 0.66 (0.49-0.96), 0.39 (0.28-0.44) and 0.17 (0.10-0.21), similar to verapamil. Concentration-response curves of CaCl₂ could be significantly moved to the right and down in the presence of STR (0.3, 1 mg/mL). Discussion and conclusions: Results suggest the presence of antidiarrheal activity and spasmolytic effects of STR, possibly mediated through CA²⁺ channel blocking activity, providing the pharmacological basis for its traditional uses in gastrointestinal disorders.