Participation of 5-HT3, 5-HT4, and nicotinic receptors in the peristaltic reflex of guinea pig distal colon.

The roles of 5-hydroxytryptamine3 (5-HT3), 5-HT4, and nicotinic receptors in the peristaltic reflex were investigated in isolated segments of guinea pig distal colon. The reflex assessed by measuring the propulsion of solid pellets, was affected neither by 5-HT3-selective antagonists (ondansetron granisetron) nor by 5-HT4-selective antagonists (SDZ-205-557, GR-113808A, SB-204070) applied individually (1.0 microM); 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 microM, but not at 10-32 microM. In contrast, the peristaltic reflex was inhibited when hexamethonium (32 microM was combined with either a 5-HT3- or 5-HT4-selective antagonist (1.0 microM). These observations suggest that 5-HT3, 5-HT4, and nicotinic receptors participate in the initiation and/or propagation of the peristaltic reflex. The data are consistent with the idea that these receptors are arranged in parallel in the neural pathways that mediate the peristaltic reflex in the distal colon.