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Abstract
The ethanolic extract of Sida pakistanica (SP) was studied for the possible presence of spasmogenic and spasmolytic constituents. SP at the dose of 0.1–5.0 mg/ml caused spasmogenic effects both in isolated guinea-pig ileum and rabbit jejunum. In the presence of atropine (0.1 µM), SP did not exhibit a spasmogenic effect, instead spasmolytic activity was enhanced at similar doses. When tested against K + -induced contraction, SP caused a dose-dependent relaxation in the concentration range of 0.3–10 mg/ml, suggestive of the involvement of calcium channel blockade (CCB). The crude extract was subjected to activity-directed fractionation to separate spasmogenic (cholinergic) and spasmolytic (CCB) constituents. The results revealed the spasmogenic component was separated in the aqueous fraction whereas the spasmolytic component was concentrated in the ethyl acetate fraction. The potent CCB effect of the ethyl acetate fraction wasln confirmed when the pretreatment of tissue with SP (0.03–0.3 mg/ml) shifted Ca ++ dose-response curves to the right in a dose-dependent manner.