alpha(1)-adrenoceptor-induced contractility in rat aorta is mediated by the alpha(1D) subtype

Adrenoceptor agonists were used to characterize the alpha(1)-adrenoceptor subtype responsible for mediating tension (phasic and tonic combined) in the denuded rat aorta and compared with radioligand binding at alpha(1)-adrenoceptor subtypes. The rank order of potency at the rat aorta was the same as that obtained for binding affinity at the rat clonal alpha(1d)-adrenoceptor: norepinephrine > epinephrine > cirazoline > phenylephrine > oxymetazoline > A-61603 > methoxamine. Correlation coefficients comparing rat aortic contraction (pD(2)) to binding (pK(i)) were 0.09-0.21 for alpha(1A/a) receptors, 0.66 for clonal alpha(1b) and 0.94 for clonal alpha(1d)-adrenoceptors. Correlation coefficients comparing the clonal alpha(1d)-adrenoceptor binding affinity to in vitro contractile responses were 0.03 and 0.10 for the rat vas deferens and canine prostate alpha(1A)-adrenoceptor responses, respectively, 0.09 for the rat spleen alpha(1B) and as noted, 0.94 for the rat aorta. The agreement observed between agonist potency at the rat aorta and affinity for the alpha(1d) binding sire provide new evidence that the alpha(1D)-adrenoceptor subtype is responsible for mediating contractions in the rat aorta.