Selective agonists reveal ?1A- and ?1B-adrenoceptor subtypes in caudal artery of the young rat

1 Multiple α1-adrenoceptors were evaluated in caudal artery of the young Wistar rat using selective agonists and antagonists. 2 Arteries were exposed to the selective α1A-adrenoceptor agonist, A-61603 (N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl] methanesulfonamide) or to phenylephrine and to prazosin (α1-adrenoceptor antagonist), or the selective α1A-adrenoceptor antagonists 5-methylurapidil, RS 100329 (5-methyl-3-[3-[4-[2-(2,2,2,-trifluoroethoxy)phenyl]-1-piperazinyl]propyl]-2,4-(1H)-pyrimidinedione), RS 17053 (N-[2(2-cyclopropylmethoxy) ethyl]-5-chloro-α, α-dimethyl-1H-indole-3-ethanamide), and the selective α1D-adrenoceptor antagonist BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5] decane-7,9-dione). 3 Results showed a 100-fold higher potency of A-61603 for the α1-adrenoceptor present in the artery, compared with phenylephrine. Prazosin displaced both agonists with high affinity, whereas 5-methylurapidil, RS 100329 and RS 17053 displaced A-61603 with high affinity, indicating the presence of α1A-adrenoceptors. 4 The selective α1A-adrenoceptor antagonists blocked phenylephrine responses with low affinity, suggesting that phenylephrine activated a second receptor population in caudal artery. 5 BMY 7378 antagonized with low affinity both A-61603 and phenylephrine-induced contractions, indicating absence of α1D-adrenoceptors in the vessel. 6 The results suggest that functional α1B-adrenoceptors are present in caudal arteries of the young Wistar rat.