No evidence of existence of functional 5-HT(1) receptors in isolated and perfused canine basilar arteries.
The vascular responses to intraluminally administered 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamine (5-CT, a 5-HT(1)-like receptor agonist), alpha-methyl-5-hydroxytryptamine (alpha-M-5-HT, a 5-HT(2) receptor agonist) were examined, compared with those to noradrenaline (NA) and potassium chloride (KCl), 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 >/= CT NA KCl. The constrictions to 5-HT, 5-CT and alpha-M-5-HT were significantly inhibited by ketanserin (a 5-HT(2) receptor antagonist), but not significantly blocked by methiothepin (a 5-HT(1) receptor antagonist). From these results, we concluded that 1) 5-HT induces a prominent vasoconstriction mainly due to an activation of 5-HT(2) receptors, 2) 5-CT-induced constriction may be mostly mediated by 5-HT(2) but not 5-HT(1) receptors, and 3) there are no functional vasodilator 5-HT receptors in the canine basilar artery.
Orz
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YI
Department of Neurosurgery, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto 390, Japan.
Tsuji
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Chiba
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