ADRENOCEPTOR MECHANISM INVOLVED IN THIOPENTAL-EPINEPHRINE-INDUCED ARRHYTHMIAS IN DOGS

The authors investigated the role of alpha1- and beta-adrenoceptors on induction of ventricular arrhythmias during thiopental anesthesia in dogs and compared with that during halothane anesthesia. Throughout th is study, arrhythmogenic threshold of epinephrine during thiopental an esthesia was designed to be comparable with that during halothane anes thesia. Phenylephrine, an alpha1-agonist, and isoproterenol, a beta-ag onist, consistently failed to provoke arrhythmias during thiopental or halothane anesthesia. The interaction between phenylephrine and isopr oterenol in inducing arrhythmias was synergistic and additive during h alothane and thiopental anesthesia, respectively, indicating that adre noceptor mechanism in thiopental-epinephrine arrhythmias is different from that in halothane-epinephrine arrhythmias. During thiopental anes thesia, incidence of arrhythmias with blood pressure elevation by epin ephrine, phenylephrine, or angiotensin II was not different, and incre asing heart rate by electrical pacing did not replace isoproterenol in the arrhythmogenic interaction between isoproterenol and phenylephrin e. The results indicate that blood pressure elevation due to the combi ned inotropic action of alpha1- and beta-adrenoceptor agonists is a cr itical factor in the genesis of thiopental-epinephrine arrhythmias.