Magnolol (MAG), 5,5-Di-2-propenyl-[1,1-biphenyl]-2,2-diol ( Fig. 1), is the major phenolic compound purified from the medical plant Cortex magnoliae officinalis, 1) which has been used for lower gastrointestinal disorders (e.g., diarrhea, constipation) in Traditional Chinese Medicine for long time.2) Major findings about the pharmacological activity of MAG involved: 1) inhibition of the respiratory burst in formylmethionyl-leucyl-phenylalanine activated neutrophils 3); 2) suppression of the overproduction of nitric oxide and tumor necrosis factor (TNF)-a in lipopolysaccharide activated macrophages ; and 5) antioxidative effect on neutrophil adhesion in vitro and in vivo in rats, [7][8][9] Furthermore, MAG has previously been reported to inhibit smooth muscle contraction in porcine trachea, with possible mechanism of blockade of calcium influx through voltage dependent Ca 2ϩ channels. 10) Recently, one study reported that MAG can inhibit contractility of the upper gastrointestinal tract smooth muscles of isolated gastric fundus strips of rats and isolated ileum of guinea pigs with a calcium-antagonistic effect, 11) but no research have been done about MAG on the lower gastrointestinal tract. The characteristics of different parts of the gastrointestinal tract are not the same, especially in terms of motility, 12) permeability, 13) and response to calcium manipulation.14) Thus, it is necessary to study the effect of MAG on colon, in order to understand the pharmacological action of MAG in lower gastrointestinal disorder.In this study, pharmacological effects of MAG on muscle strips isolated from distal colon of guinea pig were investigated with the presence of activators and inhibitors of muscle contraction, and isolated colon segments of guinea pig were used to test the effect of MAG on the velocity of artificial pellet propulsion. MATERIALS AND METHODS Tissue PreparationMale guinea pigs (200-250 g) were fasted for 24 h, and then sacrificed by stunning and cervical dislocation, and 2-cm pieces of the colon were dissected from the colon segment 1.5 to 2 cm from anus. Luminal contents were washed out with Krebs-bicarbonate buffer. The segments were then opened along the mesenteric border, cut into 10 mmϫ4 mm strips approximately along the circular and longitudinal axis individually and transferred into cold Krebs-bicarbonate buffer. The mucosa was carefully dissected away to expose the muscularis externa. Tissues were mounted for tension recording and allowed to equilibrate for 1-2 h in 10-ml chambers containing Krebs-bicarbonate buffer (118 mM NaCl, 4.8 mM KCl, 1.2 mM KH 2 PO 4 , 1.2 mM MgSO 4 , 2.5 mM CaCl 2 , 25 mM NaHCO 3 and 11 mM Glucose, pH 7.4, at 37°C), and saturated with 95%O 2 and 5%CO 2 . The colonic longitudinal muscle strips (LMS) and circular muscle strips (CMS) were initially maintained at 0.5 g tension and equilibrated for 60 min. The bath solution was replaced every 20 min to keep the solution fresh during equilibration. Measurement of Contractile ActivityThe mechanical responses in preparations w...
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