Background: Viscum album has shown inhibitory effect on different smooth muscles but underlying mechanisms in gut and vascular smooth muscles are not well defined. Additionally, the plant has also importance in managing hyperactive gut and cardiovascular disorders. The current study was aimed to probe a pharmacological base of the smooth muscle relaxant effect of V. album in gut and vascular preparations. Methods: V. album crude extract (Va. Cr) and its ethyl acetate fraction (Va. EtAc) were studied using in vitro techniques. The antispasmodic activity was performed using isolated rabbit jejunum while the vasorelaxant effects were studied in rabbit aortic rings. Results: Va. Cr and Va. EtAc inhibited spontaneous and high K+-induced contractions with EC50 values of 0.31 mg/mL (0.15-0.57) and 0.62 mg/mL (0.3-0.95), respectively. This advocates an antispasmodic effect probably operated through calcium channels blockade (CBB). The proposed mechanism was confirmed by a pretreatment of the tissue with Va. Cr (0.01-0.3 mg/mL), which shifted the Ca++ concentration-response curves (CRCs) rightward, similar to verapamil. Moreover, Va. Cr showed a partial relaxation against high K+ and PE (1 mu M) induced contractions in isolated rabbit aorta rings. Va. EtAc caused complete relaxation of high K+ precontraction and partially relaxed PE (1 mu M) induced contractions, suggesting inhibitory effect on Ca++ entry, in addition to other possible mechanisms. CRCs were shifted to the right correspondingly to verapamil when the aortic rings were pretreated with Va. Cr and Va. EtAc. Conclusions: These data indicated that Va. Cr possesses smooth muscle relaxant effect mediated through voltage-dependent Ca++ channel blockade (CCB), which explains its spasmolytic and vasorelaxant activity. The CCB activity is concentrated more in Va. EtAc. This study provides an evidence for the medicinal importance of V. album in gut spasm and possibly hypertension.
