No evidence of existence of functional 5-HT1 receptors in isolated and perfused canine basilar arteries

The vascular responses to intraluminally administered 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamime (5-CT, a 5-HT1-like receptor agonist), alpha-methyl-5-hydroxytryptamine (alpha-M-5-HT, a 5-HT2 receptor agonist) were examined, compared with those to noradrenaline (NA) and potassium chloride (KCI), in isolated and perfused canine basilar arteries using the steel cannula insertion method, These agonists usually elicited only a vasoconstriction in a dose related manner Even in preconstricted preparations by 30 and 60 mM K+ in modified Krebs solution, the injection of either 5-HT or 5-CT induced only monophasic constrictor responses without any dilation. The rank order of vasoconstrictive potency was 5-HT > alpha-M-5-HT greater than or equal to CT much greater than NA much greater than KCL. The constrictions to 5-HT, 5-CT and alpha-M-5-HT were significantly inhibited by ketanserin ( a 5-HT, receptor antagonist), but not significantly blocked by methiothepin (a 5-HT1, receptor antagonist). From these results, we concluded that 1) 5-HT induces a prominent vasoconstriction mainly due to an activation of 5-HT2, receptors, 2) 5-CT-induced constriction may be mostly mediated by 5-HT2 but not 5-HT1, receptors, and 3) there are no functional vasodilator 5-HT receptors in the canine basilar artery. (C) Pearson Professional Ltd 1997.