Regulation of contractile activity by magnolol in the rat isolated gastrointestinal tracts

This study examined the pharmacological property of magnolol, a phenolic compound purified from Magnolia officinalis, on the GI motility using the rat isolated gastrointestinal (GI) strips. Magnolol (0.3–30 μM) dose-dependently stimulated the tone and amplitude of spontaneous contractions in ileum longitudinal muscles. Magnolol at 3 μM significantly increased the contractions of jejunum longitudinal and colon circular muscles, but not the longitudinal muscle contractions in fundus, antrum and colon. Pretreatment of ileum strips with either atropine (0.5 μM) or 4-diphenyllacetoxy-N(2-chloriethyl)-piperidine (4-DAMP, 0.5 μM) dramatically inhibited the acetylcholine (ACh, 0.1 μM)- and magnolol (3 μM)-induced longitudinal muscle contractions, but they were not affected by methoctramine (0.5 μM) and hexamethonium (0.5 μM). Ondansetron (0.1 μM) and GR113808 (2 μM) significantly reduced the tone of ileum longitudinal muscle contractions stimulated by 5-HT (10 μM), but not the amplitude. Magnolol (3 μM)-induced ileum longitudinal muscle contractions, both tone and amplitude, were significantly blocked by GR113808, but not by ondansetron. Taken together, magnolol differently regulates the spontaneous GI motility according to the region of GI tracts and orientation of smooth muscles, and magnolol-induced regulation of smooth muscle contractions in rat GI strips is likely to be mediated, at least in part, by activation of ACh and 5-HT receptors, possibly the M3 and/or 5-HT4 receptors.