The influence of oxytocin on the fibrillation thresholds in rabbits.

The intravenous infusion of oxytocin in urethane anaesthetized rabbits induced marked increases of both atrial and ventricular fibrillation threshold. The heart rate and the arterial blood pressure (BP) diminished. Since there was no parallelism between the fibrillation threshold changes and those of heart rate and BP, it might be concluded that the changes of the fibrillation thresholds were very likely primary, i.e. they were due to the modifications of the electrophysiological properties of the heart. The intravenous infusion of 0.5% chlorbutol , a preservant widely used in many commercial preparations induced only minor changes of the investigated parameters.