The beta-adrenolytic component of antifibrillatory agents. Its therapeutic significance.

The anti-fibrillatory ED50-values of a series of agents were determined. Upon administration of the agents in this ED50-dose (all agents then being equieffective in their antifibrillatory action) various side effects of each of them were quantitatively measured. The measured side effects were: the negative inotropic and chronotropic action, the conduction retarding, refractory period prolonging, excitability decreasing and ectopic automaticity depressing action. The substrate for these measurements was the isolated perfused rat heart. The series of agents tested consisted of a group possessing a beta-adrenolytic component and a group in which this component was absent. We compared quantitatively the side effects induced by the one group with those induced by the other. Differences were found in their influence on contractility and conductivity but not in their influence on the other parameters. The results obtained do not support the expectation that a beta-adrenolytic component will enlarge the therapeutic range of an antifibrillatory agent.