1. α-Adrenoceptors play an important role in regulating vascular tone. [125I]BE2254, a high affinity antagonist, has been utilized to label α1-receptors in membrane preparations from rabbit aorta. [125I]BE2254 specifically labels a single class of binding sites with the characteristics of α1-receptors.
2. Catecholamines compete for [125I]BE2254 binding stereospecifically and with the characteristic α-adrenergic potency series (−)-adrenaline ≥ (−)-noradrenaline ≪ (−)-isoprenaline.
3. The α1-adrenoceptor selective antagonist prazosin is much more potent than yohimbine in competing for the [125I]BE2254 binding sites, which suggests that the α-adrenoceptor identified is predominantly of the α1 subtype.
4. The extension of radioligand binding techniques to individual rabbit aortas should simplify the study of vascular α-adrenoceptor regulation.