Antidiarrhoeal and spasmolytic activities of the methanolic crude extract of Alstonia scholaris L. are mediated through calcium channel blockade

This study was aimed to provide a pharmacological basis to the medicinal use of Alstonia scholaris as an antidiarrhoeal and antispasmodic by using in vivo and in vitro techniques. In the in vivo study the crude extract of Alstonia scholaris (As.Cr), which tested positive for the presence of alkaloids, provided 31-84% protection against castor oil-induced diarrhoea in mice at 100-1000 mg/kg doses, similar to loperamide. In isolated rabbit jejunum preparation, the As.Cr caused inhibition of spontaneous and high K⁺ (80 mM)-induced contractions, with respective EC₅₀ values of 1.04 (0.73-1.48) and 1.02 mg/mL (0.56-1.84; 95% CI), thus showing spasmolytic activity mediated possibly through calcium channel blockade (CCB). The CCB activity was further confirmed when pretreatment of the tissue with the As.Cr (0.3-1 mg/mL) caused a rightward shift in the Ca⁺⁺ concentration-response curves similar to verapamil, a standard calcium channel blocker. Loperamide also inhibited spontaneous and high K⁺ precontractions as well as shifted the Ca⁺⁺ CRCs to the right. These results indicate that the crude extract of Alstonia scholaris possesses antidiarrhoeal and spasmolytic effects, mediated possibly through the presence of CCB-like constituent(s) and this study provides a mechanistic base for its medicinal use in diarrhoea and colic.