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

The influence of plant product magnolol (0-100,m) 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 mu(M) carbachol (CCh)- and 10 mu(M) serotonin (5-HT)induced contractions at concentrations higher than 10 mu m. 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 mu(M), and totally inhibited pellet propulsion at the concentration higher than 30 mu(M). 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 InsP(3)-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.