SELECTIVE BETA-1 AND BETA-2 ADRENOCEPTOR BLOCKADE ON EPINEPHRINE-INDUCED ARRHYTHMIAS IN HALOTHANE ANESTHETIZED DOGS

Beta2 as well as beta1 adrenoceptors have been recognized in the heart of vertebrates. They mediate a positive chronotropic action of catecholamines. We compared the effect of selective beta1 and beta2 adrenoceptor antagonists on the genesis of halothane-epinephrine arrhythmias in dogs. The arrhythmogenic dose (AD) of epinephrine was increased in the presence of 1-metoprolol, a selective beta1 antagonist (8.40 +/- 1.13 mug . kg-1 . min-1; mean +/-SEM), compared with control value (2.62 +/- 0.56) (P < 0.05). In contrast, ICI-118,551, a selective beta2 antagonist, did not change the AD (2.36 +/- 0.43). Adding ICI-118,551 to 1-metoprolol did not affect the AD of epinephrine in the presence of 1-metoprolol alone (6.34 +/- 0. 74 vs 8.40 +/- 1.13). These results suggest that selective beta1 blockade is effective in preventing halothane-epinephrine arrhythmias, but selective beta2 blockade is not.