Inhibitory effects of magnolol on distal colon of guinea pig in vitro

The influence of plant product magnolol (0-100 μM) on the contractile activity of isolated colonic muscle strips in guinea pig and related mechanism were investigated. Magnolol did not affect the base tone of colon muscle strips, but it dose-dependently inhibited 40 mM KCl-, 1 μM carbachol (CCh)- and 10 μM serotonin (5-HT)-induced contractions at concentrations higher than 10 μM. And also, magnolol inhibited the 5-HT- or CCh-induced muscle contraction in calcium-free buffer. Furthermore, magnolol inhibited the KCl-induced contraction under the condition of procaine. In addition, inhibition rate of nifedipine plus magnolol on muscle strips was lower than that of nifedipine alone. Moreover, magnolol dose-dependently decreased the velocity of pellet propulsion in the concentration range of 0.1-10 μM, and totally inhibited pellet propulsion at the concentration higher than 30 μM. Thus, it can be concluded that magnolol may 1) block receptor-operated cation channels and the voltage dependent Ca²⁺ channel, and 2) inhibit calcium release from the sarcolemmal membrane (SR) through blocking InsP₃-sensitive and ryanodine-sensitive pathways. This explains, at least partially, that Cortex magnoliae officinalis exerts therapeutic effects on gastrointestinal disease through relaxation of GI tract smooth muscles.