Effect of different beta-blocking agents on an in vitro model of ventricular automaticity

The effect of 7 beta-blocking agents with different properties such as quinidine like activity (QLA) or intrinsic sympathomimetic activity (ISA) was tested on a model of automaticity induced in the isolated right ventricle of the rat. The following results were obtained: a) Propranolol was the most effective drug for the inhibition of the automatic activity; b) Pronethalol, pindolol and labetalol also decreased the automatic rate. Acebutolol was less effective than these three drugs but with larger concentrations also decreased the preparation's frequency; c) Neither sotalol nor practolol decreased the preparation's frequency, but practolol increased that frequency at higher concentrations. We conclude that QLA might play an important role in the antidysrhythmic efficacy of these compounds which might be antagonized by ISA.