[Isoproterenol potentiates atrial fibrillation induced by acetylcholine]

A perfusion with normal Tirode solution containing isoproterenol, acetylcholine and their combination into the sinus node artery of the anesthetized open-chest dogs was used to induce atrial fibrillation. The perfusion of isoproterenol, alone, was unable to induce atrial fibrillation, though significantly increased atrial rate. Meanwhile the perfusion of acetylcholine, alone, did induce atrial fibrillation in all animals. The mixed perfusion of isoproterenol and acetylcholine led to decreasing the threshold (minimum) concentration of acetylcholine to induce atrial fibrillation. Herewith, atrial fibrillation appeared at later time from a perfusion start and lasted for more long time. No significant slowing down of sinus rhythm was registered before the initiation of atrial fibrillation. The data suggest that initiation of paroxysmal atrial fibrillation may only be mediated by parasympathetic activity and dependents on a level of adrenergic activity.