Effect of 5-hydroxytryptamine on gastrointestinal motility in conscious guinea-pigs

Many studies have suggested that 5-hydroxytryptamine (5HT, serotonin) plays an important role in the control of gastrointestinal motility. However, most of these studies have been carried out on guineapig ileum in vitro. Therefore, we investigated the mechanisms of action of 5HT on gastrointestinal motility in conscious guinea-pigs. In order to investigate the effects of 5HT on gastrointestinal motility, extraluminal force transducers were sutured onto the serosal surfaces of the gastric antrum, duodenum and ileum and 5HT was infused intravenously. One of three types of 5HT antagonist or atropine was given before a 5HT infusion of 3.0 mu g kg(-1) min(-1) was started. Regular cyclic patterns were observed from the gastric antrum to the ileum in both the fasted and fed states. 5HT increased the contraction amplitudes at all sites. 5HT-induced contractions in the gastric antrum and duodenum were significantly inhibited by methy-sergide, ondansetron and atropine, but not by ketanserin. In the ileum, only atropine inhibited 5HT-induced contractions. These results suggest that 5HT increases the gastrointestinal contraction amplitude mainly via a cholinergic pathway. 5HT(3) receptors and 5HT(1)-like and/or 5HT(2C) receptors appear to be responsible for 5HT-induced gastric antral and duodenal contractions, but 5HT receptors other than 5HT(1)-like, 5HT(2A), 5HT(2C) and 5HT(3) receptors induce ileal contractions.