AND FEICENBAUM, H.: Effect of acetylcholine and potassium on repolarization of the heart

Acetylcholine has been shown to have an effect on the action potentials of mammalian atrial muscle, the sinoatrial and the atrioventricular nodes, and on the action potential of frog ven-tricles (1-4). On the other hand, the action po-tential of mammalian ventricle has been found to be highly resistant to acetylcholine. Only very slight changes were noted in the presence of enor-mous concentrations of the drug (4-6). The purpose of this communication is to pre-sent electrocardiographic evidence indicating a) that acetylcholine exerts a consistent effect on re-polarization of the ventricles in the intact dog and that this effect is independent of the heart rate, ventricular arrhythmias, and atrioventricular (AV) or intraventricular conduction delays, and b) that the effect of acetylcholine on repolariza-tion is augmented by increasing the level of plasma potassium (K). Methods Eleven experiments were performed with seven mon-grel dogs weighing 10 to 14 kg. The animals were anesthetized with either pentobarbital, 30 mg per kg iv, or a combination of morphine sulfate, 2.5 mg per kg im, followed by pentobarbital, 15 mg per kg iv. Ventila-tion was maintained through the use of a Harvard respirator. A bilateral cervical vagotomy was per-formed, and an arterial catheter was placed just above the aortic valves. Blood pressure was continuously re-corded through a Cournand needle in the femoral artery. The entire experiment was monitored with an oscilloscope, and permanent records were obtained with a direct-* Submitted for publication January 10, 1964; ac