Background: Traditional Japanese medicine, known as Kampo medicine, consists of mixtures of several medicinal herbs widely used to treat upper gastrointestinal disorders in Japan. Rikkunshito, one of these medicines, has not been evaluated with respect to its influence on gastrointestinal motor activity. We investigated the effect of rikkunshito on upper gastrointestinal motility and plasma ghrelin concentrations in conscious dogs. Methods: Contractile response to intragastric administration of rikkunshito was studied via surgically implanted force transducers. A powdered extract of rikkunshito (1.3, 2.7, and 4.0 g) dissolved in water was administered into the stomachs of normal and vagotomized dogs before feeding and gastric emptying was evaluated. Several inhibitors of gastrointestinal motility (atropine, hexamethonium, and ondansetron) were injected intravenously before intragastric administration of rikkunshito. Plasma acylated ghrelin levels after intragastric administration of rikkunshito were measured. Results: In a fasting state, intragastric administration of rikkunshito induced phasic contractions in the duodenum and jejunum in normal dogs. Rikkunshito-induced contractions were inhibited by atropine, hexamethonium and ondansetron. In vagotomized dogs, rikkunshito induced phasic contractions, similar to normal dogs. Gastric emptying was accelerated by intragastric administration of rikkunshito in a dose-dependent manner. The plasma acylated ghrelin level 150 min after intragastric administration of 4.0 g of rikkunshito was significantly higher than the control value. Conclusions: Intragastric administration of rikkunshito stimulates gastrointestinal contractions in the interdigestive state through cholinergic neurons and 5-HT type 3 receptors. Moreover, rikkunshito increases plasma acylated ghrelin levels. Rikkunshito may alleviate gastrointestinal disorders through its prokinetic effects.
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