Receptor mechanisms for 5-hydroxytryptamine in rabbit arteries.
1 Previous investigations into the vascular actions of biogenic amines implicated in migraine have shown that the contractile effects of both 5-hydroxytryptamine (5-HT) and noradrenaline (NA) in the rabbit ear artery are mediated by a direct sympathomimetic action at alpha-adrenoceptors, while in the rabbit aorta, 5-HT and NA act on pharmacologically distinct receptors. The purpose of the present investigation was to determine whether the absence of 5-HT receptors in rabbit ear arteries is characteristic of distributing arteries in general, or is confined to particular regional circulations.2 Agonist-antagonist interactions were studied in various rabbit vascular preparations (common carotid, external carotid and femoral arterial strips, and perfused ear arteries) by determining pA(2) values for pizotifen and phentolamine against 5-HT- and NA-induced contractile responses.3 In common carotid and femoral arteries, pizotifen was a potent competitive antagonist of 5-HT, but weak against NA. The converse applied to phentolamine. In external carotid and ear arteries, pizotifen was a weak competitive antagonist of both 5-HT and NA, whereas phentolamine was a potent competitive antagonist of both. Cocaine did not influence pA(2) values against NA.4 5-HT and NA were of similar potency in common carotid and femoral arteries, but 5-HT was much less potent than NA in external carotid and ear arteries.5 The results indicate that rabbit common carotid and femoral arteries contain both D-type 5-HT receptors and alpha-adrenoceptors, as does the aorta. However, external carotid arteries, like ear arteries, do not contain specific 5-HT receptors. The action of 5-HT in the external carotid artery is mediated by alpha-adrenoceptors; this is a direct sympathomimetic action since it was not inhibited by cocaine or reserpine-pretreatment.6 The absence of 5-HT receptors in the rabbit extracranial circulation may limit the usefulness of this species as a model for research relating to migraine.
D000818:Animals; D001158:Arteries / Q000187:drug effects* / Q000294:innervation; D002339:Carotid Arteries / Q000187:drug effects; D003042:Cocaine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005263:Femoral Artery / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D013564:Sympathetic Nervous System / Q000502:physiology
D011942:Receptors, Adrenergic, alpha; D011985:Receptors, Serotonin; D012701:Serotonin; D003042:Cocaine; D009638:Norepinephrine