Presence of cholinergic and calcium channel blocking activities explains the traditional use of Hibiscus rosasinensis in constipation and diarrhoea

The aqueous-ethanolic extract of the aerial parts of Hibiscus rosasinensis Linn. (Malvaceae) was studied for the possible presence of spasmogenic and spasmolytic constituents to rationalize its traditional use in gastrointestinal disorders. The crude extract (Hr.Cr) caused a concentration-dependent (1-10 mg/mL) spasmogenic effect in isolated guinea-pig ileum, which was blocked in the presence of atropine (0.1 μM). In spontaneously contracting rabbit jejunum, the plant extract exhibited a weak stimulatory effect at lower doses (0.03-0.30 mg/mL) followed by an inhibitory effect at higher doses (1.0-3.0 mg/mL). Pretreatment of the tissues with atropine blocked the stimulatory effect resulting in the potentiation of the spasmolytic effect. Hr.Cr (0.03-1.0 mg/mL) also showed an inhibitory effect on K+ (80 mM)-induced contractions. The calcium channel blocking activity was confirmed when Hr.Cr shifted the Ca2+ concentration-response curves to the right, similar to verapamil. Activity-directed fractionation revealed that the spasmolytic component(s) was separated in the ethyl acetate, while the spasmogenic in the petroleum ether fraction. The aqueous fraction exhibited a combination of weak spasmogenic and spasmolytic effects. These data indicate that the crude extract contains spasmogenic and spasmolytic constituents mediating their effect through cholinergic receptors activation and blockade of Ca2+ influx, respectively, which may explain its traditional use in constipation and diarrhoea.