Functional 5-HT receptor subtypes in the isolated canine common carotid artery

The vascular responses to 5-hydroxytrypamine (5-HT), 5-carboxamidotryptamine (5-CT, a selective 5-HT1-like receptor agonist), alpha-methyl-5-HT (alpha-M-5-HT, a relatively selective 5-HT2 receptor agonist), noradrenaline (NA), and KCl were examined in isolated, cannulated, and perfused canine common carotid arterial preparations. They caused strong vasoconstrictions. The rank order of vasoconstrictive potency was 5-HT > alpha-M-5-HT > or = NA > 5-CT >> KCl. The 5-HT-induced vasoconstriction was significantly depressed by methysergide (a 5-HT1 and 5-HT2 receptor antagonist), ketanserin (a selective 5-HT2 receptor antagonist), and spiperone (a selective 5-HT2 receptor antagonist). The 5-CT- and alpha-M-5-HT-induced vasoconstrictions were also significantly inhibited by methysergide, spiperone, and ketanserin. The NA-induced vasoconstriction was readily inhibited by bunazosin (an alpha-adrenoceptor antagonist) and ketanserin but not significantly inhibited by spiperone and methysergide. KCl has a weak potency for producing a vasoconstriction of the canine common carotid artery. A relatively large dose of diltiazem (a calcium channel-blocker) did not modify 5-HT-induced vasoconstrictions.(ABSTRACT TRUNCATED AT 250 WORDS)