Beer congener stimulates gastrointestinal motility via the muscarinic acetylcholine receptors

Background: Ethanol and alcoholic beverages are known to affect upper gastrointestinal motility in humans. Beer has been reported to accelerate gastric emptying compared with other beverages that contain the same ethanol concentrations. In this study, we investigated the mechanism that underlies the effects of beer congener on gastrointestinal motility. Methods: Gastric emptying activity was measured by means of movement of a semisolid test meal (0.05% phenol red/1.5% methylcellulose) in mice. To elucidate the mechanism for the effect of beer congener on gastrointestinal motility, we conducted receptor binding assays and contraction study by using longitudinal muscle from guinea pig ileum. Results: Beer congener (1 g/kg orally) enhanced gastric emptying of a semisolid meal in mice. The receptor binding assay revealed that beer congener bound to dopamine D-2 receptor and 5-hydroxytryptamine (5-HT)(3) receptor. These IC50 values were more than 5 mg/ml. However, beer congener bound to 5-HT2 receptor, 5-HT4 receptor, and muscarinic M-3 receptor with IC50 values of 2, 0.9, and 2 mg/ml, respectively. Beer congener (0.05-2 mg/ml) induced the contraction of longitudinal muscle from guinea pig ileum in a dose-dependent manner. This effect was not affected by either tetrodotoxin (10(-6)M) or ketanserin (10(-7)-10(-5)M), an antagonist for the 5-HT2 receptor. On the other hand, 4-DAMP (10(-8)-10(-5)M), an antagonist for the muscarinic M-3 receptor, inhibited the contraction of the longitudinal muscle induced by beer congener (2 mg/ml) dose dependently. Conclusions: Beer congener stimulates gastrointestinal motility via the muscarinic M-3 receptor.