5-HT(1B)-RECEPTORS MEDIATE POTENT CONTRACTILE RESPONSES TO 5-HT IN RAT CAUDAL ARTERY

5-Hydroxytryptamine (5-HT) evoked potent contractile responses in phenoxybenzamine-treated ring segments of rat caudal artery, partially contracted with U46619. Responses were mimicked by 5-HT1-selective agonists with the potency order: RU24969>5-carboxamidotryptamine>5-HT=CP-93,129 >>sumatriptan. 8-Hydroxy-N,N-dipropylaminotetralin was virtually inactive. Responses were unaffected by spiperone (0.1 muM) and mesulergine (1.0 muM), but were antagonized competitively by (+/-)-cyanopindolol affording agonist-independent pK(B) estimates of 8.4 to 8.9. The pharmacological profile of this receptor is consistent with that of the 5-HT1B subtype. Since the 5-HT1B receptor is the rodent homologue of the 5-HT1Dbeta subtype, it might be anticipated that 5-HT1Dbeta receptors will be found to mediate vasoconstrictor responses in non-rodent species.