Peppermint Aqueous Extract Counteracts Smooth Muscle Contraction in Rat Ileum

Peppermint is widely used for gastrointestinal disorders; however, its pharmacological action on isolated rat ileum has not yet been evaluated. In this study, the effect of peppermint aqueous extract was investigated for its ability to reduce rat illial smooth muscle contractility induced by acetylcholine (Ach) and potassium chloride (KCl). The experiments were conducted using an organ bath apparatus. A section of rat ileum was suspended in an organ bath containing Tyrode’s solution. The tissue was stimulated with either Ach or KCl. The tissue was kept under 1 g tension at 37°C and continuously gassed with O2. Illial smooth muscle contractility was studied in the absence and presence of peppermint. Peppermint aqueous extract prevented illial smooth muscle contractility induced by both Ach and KCl. The aqueous extract of peppermint (1g/ml) caused a rightward shift of the Ach dose response curve and brought about a decrease in the maximum response. This extract also produced a rightward shift in the KCl dose response curve but without affecting the maximum response. These results indicate that peppermint aqueous extract counteracts Ach and KCl induced smooth muscle contractility in rat ileum. The results also suggest that the peppermint effect on Ach induced contractility was non competitive in nature. The reduction in KCl induced contractility also indicates that peppermint aqueous extract was at least partially mediated by its effect on illial smooth muscle calcium channels.