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Characterization of 5‐HT receptors mediating contraction of canine and primate basilar artery by use of GR43175, a selective 5‐HT1‐like receptor agonist

1 The aim of this study was to characterize the 5‐hydroxytryptamine (5‐HT) receptor which mediates contraction of canine and primate isolated basilar artery by use of a variety of selective 5‐HT agonists and antagonists. 2 5‐HT, α‐methyl 5‐HT and the selective 5‐HT1‐like receptor agonists, GR43175 and 5‐carboxamidotryptamine (5‐CT), each caused contraction of canine and primate basilar artery with a rank order of agonist potency of 5‐CT ≥ 5‐HT > GR43175 > α‐methyl 5‐HT. The 5‐HT1‐like receptor agonists, GR43175 and 5‐CT, produced maximum effects which were less than that produced by 5‐HT or α‐methyl 5‐HT. 3 In canine basilar artery, ketanserin (0.1–1 μm) caused some depression of the maximum effect of 5‐HT but produced little or no shift of the concentration‐effect curve. The contractile effects of GR43175 were not modified by ketanserin (1 μm), MDL72222 (1 μm) or cyanopindolol (1 μm). However, the effects of 5‐HT and GR43175 were specifically antagonized by methiothepin (0.1 μm); the mean agonist concentration‐ratios were 33 and 48 respectively. 4 In primate basilar artery, ketanserin (1 μm) again caused a small depression of the 5‐HT maximum response but had no effect against GR43175‐induced contractions. In contrast, methiothepin (0.1 μm) antagonized both 5‐HT‐ and GR43175‐induced contractions; the mean agonist concentration‐ratios were 35 for both. 5 These results demonstrate that a large component of the effects of 5‐HT in canine and primate basilar artery is produced by stimulation of a 5‐HT1‐like receptor. This receptor can be characterized by the high potency of the novel, selective agonist, GR43175, and susceptibility to blockade by methiothepin. However, there also appears to be a population of 5‐HT2 receptors in these pre‐pAarations which contribute to the contractile effects of 5‐HT.