AUTORADIOGRAPHIC LOCALIZATION OF BETA-ADRENERGIC RECEPTORS IN HUMAN LARGE CORONARY-ARTERIES

The distribution of beta-adrenergic receptors in sections of the human right and left coronary arteries and of the anterior intraventricular branch was studied by the use of combined in vitro radioreceptor binding and autoradiographic techniques. [I-125]Cyanopindolol was used as a ligand for beta-adrenergic receptors. Binding of the radioligand to sections of the three coronary arteries under study was saturable, stereoselective, reversible, and displaceable by antagonists and agonists with the rank order of potency expected for beta-adrenergic receptors. Analysis of binding isotherms indicated maximum binding capacities of 41.5 fmol/mg protein for the right coronary artery, 35.4 fmol/mg protein for the left coronary artery, and 25.7 fmol/mg protein for the anterior interventricular branch. Dissociation constants were approximately 35 pM in the arteries examined. The relative amounts of beta-1 and beta-2-receptor subtypes were as follows: 72% beta-1-receptors and 28% beta-2-receptors in the right coronary artery; 65% beta-1-receptors and 35% beta-2-receptors in the left coronary artery; 40% beta-1-receptors and 60% beta-2-receptors in the anterior interventricular branch. The results of autoradiographic analysis revealed a predominance of beta-1-receptors in the medial layer. beta-2-Receptors were localized primarily in the adventitia, in the adventitia-media border, and in the intimal layer. These results should lead to a better understanding of the mechanisms involved in the control of coronary circulation in humans.