Relaxant response of goat trachea to 5-hydroxy-tryptamine mediated by D-tryptamine receptors.
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 beta-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 alpha-adrenoceptors; and (iii) predominance of H(1)-histamine receptors in the goat trachea.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002927:Cimetidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006041:Goats; D007213:Indomethacin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008785:Metiamide / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D014132:Trachea / Q000187:drug effects / Q000502:physiology*
D011985:Receptors, Serotonin; D012701:Serotonin; D008785:Metiamide; D001285:Atropine; D002927:Cimetidine; D011433:Propranolol; D007545:Isoproterenol; D007213:Indomethacin