Effects of bufetolol on rat heart and liver adenyl cyclase activities

Abstract

The effect of bufetolol, a β-adrenergic blocking agent, on the activities of the adenyl cyclase of rat heart (β1) and liver (β2) was examined. Bufetolol did not activate adenyl cyclase of the heart at concentrations from 10-5 to 10-10M, but showed a slight inhibition at high concentrations. Bufetolol inhibited the activation of heart adenyl cyclase by 10-5M epinephrine or isoproterenol at above 10-9 or 10-6M, respectively, but did not inhibit the activation by 3μg/ml of glucagon or 10-3M of NaF. The inhibition of Bufetolol against isoproterenol was shown to be competetive from Lineweaver-Burk analysis. Bufetolol did not affect the basal activity of the liver adenyl cyclase. With the activation by 10-5M epinephrine, bufetolol inhibited it at 10-6M or higher concentrations. The activities of phosphodiesterase and Mg2+, Na+, K+-adenosine triphosphatase of rat heart or protein kinase of rabbit skeletal muscle were not affected by bufetolol. These results suggest that the β-adrenergic blocking activity of Bufetolol is shown by the inhibition of the activation of adenyl cyclase in competition with catecholamines at β-receptor sites.