The affinity of betaxolol, a β1‐adrenoceptor‐selective blocking agent, for β‐adrenoceptors in the bovine trachea and heart

Abstract

The specificity of betaxolol, a β‐adrenoceptor antagonist, for β1 and β2‐adrenoceptors was compared with that of other β‐antagonists, atenolol, ICI‐118551, butoxamine and (±)‐propranolol, in the bovine trachea and heart by competitive interaction with [3H]‐CGP12177 as a radioligand. The radioligand Kd values were 0.75 ±0.12 and 1.60 ± 0.11 nm in the trachea and heart, respectively, and the Bmax values were 34.00 ± 4.41 and 21.54 ± 2.94 fmol mg−1 protein, respectively. Using ICI‐118551, we determined the ratio of β1:β2‐adrenoceptors in the trachea and heart to be approximately 29:71 and 56:44, respectively. In the trachea, a β2‐predominant tissue, betaxolol and atenolol were more selective for β1‐adrenoceptor binding sites than β2‐adrenoceptor binding sites, whereas ICI‐118551 and butoxamine were more selective for β2‐adrenoceptor binding sites. The β1‐selectivity of betaxolol was 2.2 and 2.7 fold higher than that of atenolol in the bovine trachea and heart. These findings suggest that betaxolol may be useful in the treatment of hypertension, cardiac arrhythmia and angina pectoris. 1993 British Pharmacological Society