Pharmacological characterization of postsynaptic alpha-adrenoceptor subtypes in five different dog arteries in-vitro

The responses of helically cut strips of arteries isolated from five different sites in the body of dogs to relatively selective alpha 1- and alpha 2-adrenoceptor agonists and the antagonism exerted on these responses by relatively selective alpha 1- and alpha 2-adrenoceptor blockers have been studied. On all arteries (renal, splenic, cranial mesenteric, jejunal and femoral) phenylephrine was a full agonist whereas UK-14,304 was a partial agonist causing maximal contractions of 49, 30, 27, 27 and 10% of the maximum, respectively. Phenylephrine was more potent than UK-14,304, being 9 times more potent in the renal artery and up to 42 times more potent in the cranial mesenteric artery. In the dog saphenous vein, where there are both alpha 1- and alpha 2-adrenoceptors, it has been previously shown that UK-14,304 is 530 times more potent than phenylephrine. Prazosin in low concentrations displaced concentration-response curves for both phenylephrine and UK-14,304 (pA2 values of 8.16-8.43 and 8.13-8.79, respectively) whereas yohimbine was much less potent (pA2 values of 6.53-6.88 and 6.50-7.20, respectively). The results suggest that the alpha-adrenoceptors of all arteries studied are predominantly, if not exclusively, of the alpha 1-subtype.