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RELAXANT RESPONSE OF GOAT TRACHEA TO 5‐HYDROXYTRYPTAMINE MEDIATED BY D‐TRYPTAMINE RECEPTORS
Author(s) -
CHAND N.,
DeROTH L.,
EYRE P.
Publication year - 1979
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1979.tb13684.x
Subject(s) - carbachol , histamine , chemistry , phenylephrine , endocrinology , propranolol , isoprenaline , medicine , methysergide , atropine , histaminergic , mepyramine , pharmacology , prazosin , antagonist , receptor , stimulation , blood pressure
1 Goat isolated trachea contracted in response to carbachol, histamine and 2‐pyridylethylamine (an H 1 ‐receptor agonist) and relaxed after application of isoprenaline, 5‐hydroxytryptamine (5‐HT) and phenylephrine. 2 Mepyramine, a selective H 1 ‐receptor antagonist, blocked histamine‐ and 2‐pyridylethylamine‐induced contractions. In high doses it also exhibited some nonspecific antagonism to carbachol. After H 1 ‐receptor blockade, 4‐methylhistamine and dimaprit (specific H 2 ‐agonists) relaxed the carbachol‐contracted trachea. 3 Propranolol, a β‐adrenoceptor blocker, antagonized relaxation in response to isoprenaline and phenylephrine. In high doses, it produced a reversal of the phenylephrine response. 4 Indomethacin enhanced contractions in response to carbachol and histamine. 5 Relaxation to 5‐HT was not affected by propranolol, indomethacin, metiamide or cimetidine (H 2 ‐blockers). These findings appear to exclude the involvement of adrenergic, prostaglandinergic and H 2 ‐histaminergic mechanisms in the mediation of this response. 6 Atropine potentiated 5‐HT‐induced relaxations. This suggests the participation of a ‘masked’ excitatory cholinergic mechanism. 7 Methysergide, dibenamine and dibenzyline selectively antagonized or reversed 5‐HT‐induced relaxation. Dibenamine and dibenzyline enhanced relaxations to isoprenaline. 8 This investigation showed (i) a relaxant response of goat trachea to 5‐HT, mediated via D‐muscular tryptamine receptors; (ii) a small population of excitatory M‐neuronal tryptamine and α‐adrenoceptors; and (iii) predominance of H 1 ‐histamine receptors in the goat trachea.