PARTICIPATION OF 5-HT3, 5-HT4, AND NICOTINIC RECEPTORS IN THE PERISTALTIC REFLEX OF GUINEA-PIG DISTAL COLON

The roles of 5-hydroxytryptamine(3) (5-HT3), 5-HT4, and nicotinic rece ptors in the peristaltic reflex were investigated in isolated segments of guinea pig distal colon. The reflex, assessed by measuring the pro pulsion of solid pellets, was affected neither by 5-HT3-selective anta gonists (ondansetron, granisetron) nor by 5-HT4-selective antagonists (SDZ-205-557, GR-113808A, SE-204070) applied individually (1.0 mu M); nevertheless, the reflex was inhibited by combining these antagonists or by applying a 5-HT3/5-HT4 dual antagonist (FK-1052). Hexamethonium abolished the peristaltic reflex at 100 mu M, but not at 10-32 mu M. I n contrast, the peristaltic reflex was inhibited when hexamethonium (3 2 mu M) was combined with either a 5-HT3- or 5-HT4-selective antagonis t (1.0 mu M). These observations suggest that 5-HT3, 5-HT4, and nicoti nic receptors participate in the initiation and/or propagation of the peristaltic reflex. The data are consistent with the idea that these r eceptors are arranged in parallel in the neural pathways that mediate the peristaltic reflex in the distal colon.