the effects of serotonin receptor antagonists on contraction and relaxation responses induced by electrical stimulation in the rat small intestine

conclusions the application of 5-ht1a, 5-ht2, 5-ht3, 5-ht4, 5-ht6 and 5-ht7 receptor antagonists, applied at concentrations lower than 1.0 µm did not modify the efs-induced contraction and relaxation responses, whichsuggests the unlikely involvement of endogenous 5-ht in mediating responses to efs in the described test conditions. materials and methods segments taken from the rat duodenum, jejunum, mid and terminal ileum were vertically mounted, connected to a transducer and exposed to efs with different frequencies in the absence and presence of various inhibitors of enteric mediators i. e. specific 5-ht receptor antagonists. results efs-induced responses were sensitive to ttx and partly to atropine, indicating a major neuronal involvement and a cholinergic system. pre-treatment with way100635 (a 5-ht1a receptor antagonist) and granisetron up to 10.0 µm, gr113808 (a 5-ht4 receptor antagonist), methysergide and ritanserin up to 1.0 µm, failed to modify responses to efs inall examined tissues. in the presence of sb258585 1.0 µm (a 5-ht6 receptor antagonist) there was a trend to enhance contraction in the proximal part of the intestine and reduce contraction in the distal part. pre-treatment with sb269970a 1.0 µm (5-ht7 receptor antagonist) induced a greater contractile response to efs at 0.4 hz only in the duodenum. background the main source of 5-ht in body is in enterchromafin cells of intestine, different studies mentioned different roles for endogenous 5-ht and receptors involved and it is not clearified the mechanism of action of endogenous 5-ht. objectives to study the role of endogenous 5-ht on modulation of contraction and relaxation responses induced by electrical field stimulation (efs) in different regions of the rat intestine.