Existence of Functional α1A- and α1D- but No α1B-Adrenoceptor Subtypes in Rat Common Carotid Arteries

Using the cannula inserting method, vasoconstrictor responses to α1-adrenoceptor agonists (noradrenaline [NA], phenylephrine [PE] and methoxamine [ME]) and effects of α1-adrenoceptor antagonists (WB4101, chloroethylclonidine [CEC] and BMY7378) were investigated in isolated and perfused rat common carotid arteries. The rank order of agonist potency and efficacy was NA = PE > ME. Either WB4101 or BYM7378 inhibited NA- and PE-induced constrictions in a dose-related manner. CEC did not inhibit the NA- and PE-induced responses. The ME-induced responses were also significantly blocked by either WB4101 or BMY7378. From these results, it is concluded that there are functional α1A- and α1D-adrenoceptor subtypes in rat common carotid arteries, but no functional α1B subtype.