2-Methyl-5-HT-induced vasoconstrictions mediated via alpha 1-adrenoceptors in rabbit common carotid arteries.

We investigated the effects of 2-methyl-5-HT and 1-phenylbiguanide on isolated and perfused rabbit common carotid arteries by a cannula insertion method. 1-Phenylbiguanide produced neither vasoconstriction nor dilation. On the other hand, 2-methyl-5-HT produced only a vasoconstriction, and the dose-response curve was shifted to the right in parallel by treatment with either ketanserin or bunazosin, although methysergide and granisetron had no antagonistic effect. Moreover, the vasoconstriction was not inhibited by guanethidine and imipramine. These data showed that 2-methyl-5-HT acts as an alpha 1-adrenoceptor agonist but not as a 5-HT3-receptor agonist in this vessel.