Evidence for mediation by 5-HT2 receptors of 5-hydroxytryptamine-induced contraction of canine basilar artery.

The agonist potencies of 8 indole derivatives and the potencies of 19 recognized antagonists to inhibit constrictor responses to 5-hydroxytryptamine (5-HT) of canine basilar artery were established. In addition the affinities of the indole derivatives for [3H]5-hydroxytryptamine [( 3H]5-HT) binding sites and the affinities of the antagonists for [125Iodo]LSD [( 125I]LSD) binding sites in rat brain cortex membranes were determined. Comparison was also made between the potencies of the antagonists on canine basilar artery and the KD values published for displacement of [3H]ketanserin binding (Leysen et al. 1982). There was a good correlation between the affinities of the antagonists for 5-HT2 binding sites labelled by both [125I]LSD and [3H]ketanserin and the affinity parameters calculated for inhibition of constrictor responses to 5-HT of canine basilar artery. No correlation could be found between the affinities of the indole derivatives for 5-HT1 binding sites labelled by [3H]5-HT and their potencies to constrict canine basilar artery. It is concluded that constrictor responses to 5-HT of canine basilar artery are mediated by 5-HT2-like receptors.