Selective adrenergic beta-receptor blockade in the prevention of adrenaline-evoked ventricular arrhythmias in dogs anaesthetized with halothane in oxygen.

The effect of selective beta-receptor blockade on adrenaline-evoked ventricular arrhythmias was studied in atropinized dogs anaesthetized with halothane in oxygen. Cardiac beta-receptors were selectively blocked with ICI 50172, while the peripheral vascular beta-receptors were selectively blocked with H 35/25. ICI 50172 prevented adrenaline-evoked ventricular arrhythmias and the increase in sinus rate produced by adrenaline. The blockade produced was surmountable, larger doses of adrenaline increasing the rate of sinus rhythm and then ventricular arrhythmias followed. In contrast H 35/25 showed only a weak anti-arrhythmic activity. This action appears to be non-specific, since the increase in sinus rate caused by adrenaline was only partially prevented by H 35/25. The results are in agreement with the concept that ICI 50172 blocks excitatory beta-receptors, while H 35/25 blocks inhibitory beta-receptors.