Comparative study of beta andreoceptor antagonists on the isolated atria of control and of the reserpine treated rabbits.

The effect of four adrenoceptor antagonists, chosen because of reported differences in their selectivities, were compared using the positive chronotropic response to isoprenaline on isolated rabbit atria. Oxprenolol was the most potent antagonist of the isoprenaline induced cardiac arrhythmias. Alprenolol, practolol and propranolol also blocked the positive chronotropic responses to isoprenaline effectively. All the antagonists lowered the resting heart rate. The effects of all four selected antagonists on heart rate probably result from cardiac beta adrenoceptor blockade. Atria isolated from reserpine treated rabbits, showed a reduced percentage of increase in the heart rate in response to addition of isoprenaline. This decreased response has been related in some cases to direct myocardial inhibition.