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

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Abstract
The responses of helically cut strips of arteries isolated from five different sites in the body of dogs to relatively selective α1- and α2-adrenoceptor agonists and the antagonism exerted on these responses by relatively selective α1 - and α2-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 α1- and α2-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 α-adrenoceptors of all arteries studied are predominantly, if not exclusively, of the α1-subtype.

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