Direct measurement of vascular alpha 1-adrenoceptors.

alpha-Adrenoceptors play an important role in regulating vascular tone. [125I]BE2254, a high affinity antagonist, has been utilized to label alpha 1-receptors in membrane preparations from rabbit aorta. [125I]BE2254 specifically labels a single class of binding sites with the characteristics of alpha 1-receptors. Catecholamines compete for [125I]BE2254 binding stereospecifically and with the characteristic alpha-adrenergic potency series (-)-adrenaline greater than or equal to (-)-noradrenaline much greater than (-)-isoprenaline. The alpha 1-adrenoceptor selective antagonist prazosin is much more potent than yohimbine in competing for the [125I]BE2254 binding sites, which suggests that the alpha-adrenoceptor identified is predominantly of the alpha 1 subtype. The extension of radioligand binding techniques to individual rabbit aortas should simplify the study of vascular alpha-adrenoceptor regulation.