Abstract
The present study was designed to demonstrate the existence in canine aorta of α1-adrenoceptor subtypes, α1High and α1Low, that have different binding affinities for 3H-prazosin and to assess the binding affinity of several drugs for each subtype by a displacement experiment. A radioligand binding assay with 3H-prazosin revealed the presence of two α1-adrenoceptor subtypes in the canine aorta. One of them which has a high affinity for prazosin was designated as α1High (Kd: 12.40 pM, Bmax: 21.88 fmol/mg protein), and the other type was designated as α1Low(Kd: 506.03 pM, Bmax: 88.22 fmol/mg protein). The pKi values of several drugs for each subtype were determined, and all drugs used in the present study, except for benoxathian and chlorethylclonidine, showed significant differences between the pK1 values for α1High and those for α1Low. Although it is difficult to characterize each α1High and α1Low into α1A or α1B by only the displacement potency, one structural characteristic to distinguish between α1High and α1Low could be evaluated.
