(bā'tă ad'rĕ-nĕr'jik rĕ-sep'tŏrz) Adrenergic receptors in effector tissues capable of selective activation by isoproterenol and blockade by propranolol. Their activation results in physiologic responses such as increases in cardiac rate and force of contraction (β1), and relaxation of bronchial and vascular smooth muscle (β2).