5-HYDROXYTRYPTAMINE(4) RECEPTOR AGONISTS INITIATE THE PERISTALTIC REFLEX IN HUMAN, RAT, AND GUINEA-PIG INTESTINE

Background & Aims: The peristaltic reflex induced by mucosal stimuli i s mediated by intrinsic sensory calcitonin gene-related peptide (CGRP) neurons activated by 5-hydroxytryptamine (5-HT) released from enteroc hromaffin cells. The involvement of 5-HT4 receptors was examined with selective 5-HT4 agonists. Methods: Compartmented intestinal segments w ere used to measure neurotransmitter release and the mechanical compon ents of the reflex. Results: In human jejunal and rat and guinea pig c olonic segments, addition of the 5-HT4 agonist HTF 919 elicited releas e of CGRP only into the compartment where the 5-HT4 agonist was added; vasoactive intestinal peptide (VIP) was released only into the compar tment where descending relaxation was measured, and substance P (SP) w as released only into the compartment where ascending contraction was measured. The CGRP antagonist hC-GRP8-37 inhibited both mechanical res ponses by 75%-80%. Release of CGRP, VIP, and SP as well as ascending a nd descending responses were inhibited by selective 5-HT4 but not by s elective 5-HT3 antagonists. Similar results were obtained with a diffe rent 5-HT4 agonist, R093877. However, HTF 919 was 10-30 times more pot ent (median effective concentration, similar to 10 nmol/L for peptide release and 5 nmol/L for mechanical responses) than R093877. Conclusio ns: Selective 5-HT4 agonists applied to the mucosa in nanomolar concen trations trigger the peristaltic reflex in human, rat, and guinea pig intestine.