Receptors implicated in the actions of serotonin on chicken ileum longitudinal smooth muscle

M. T. Martin, A. G. Fernández, E. Fernández, E. Goñalons

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    Abstract

    The presence of serotonin (5-HT) in the chicken gastrointestinal tract has been previously reported, but its motor effects have been poorly described. The aims of this work were: A) to define the effects of 5-HT on chicken longitudinal ileum; B) to explore the mechanisms by which such effects occur and C) to identify the subtype(s) of 5-HT-ergic receptors implicated. The motor responses to 5-HT were assayed in vitro using ileal strips taken from male White Leghorb chickens 7-9 week old. 5-HT elicited ileal contraction (EC50 9.6 × 10-8 M), which was markedly decreased in the presence of tetrodotoxin (TTX). Repeated exposure of the tissue to supramaximal concentrations of 5-HT did not however lead to desensitization. Atropine (10-6M), ketanserin (10-5 M), methysergide(10-5 M) and methiothepine (10-6 M), attenuated the response to 5-HT. Ketanserin was an effective inhibitor of the residual response to 5-HT obtained even in the presence of TTX. Several serotogenic agonists were assayed to further analyse the type to receptors involved in the response to 5-HT. 5-methoxytryptamine (5-MOT), a mixed 5-HT1, 5-HT2 and 5-HT4 agonist, reproduced all the effects of 5-HT. 8-OH-DPAT, a selective 5-HT1A agonist, trifluoromethylphenylpiperazine, a mixed 5-HT1B/C agonist, and m-chlorophenylbiguanide, a 5-HT3 agonist, did not induce any consistent contractile effectss. Sumatriptan, a 5- HT1D agonist, exerted a slight agonistic effect which was blocked by methiothepine and decreased by TTX but not by atropine. Cisapride, a 5 -HT4 partial agonist in mammals, decreased the effects of both 5-HT and 5-MOT. These results indicate that chicken ileum contains 5-HT1 receptors similar to the 5-HT1D mammalian subtype but not the 5-HT1A, 5-HT1B, 5-HT1C or 5-HT3 subtypes. 5-HT2 receptors are also present and would appear to be located on smooth muscle. © 1993.
    Original languageEnglish
    Pages (from-to)1361-1369
    JournalLife Sciences
    Volume52
    DOIs
    Publication statusPublished - 1 Jan 1993

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