EFFECT OF PROPRANOLOL ON CATECHOLAMINE-INDUCED ARRHYTHMIAS DURING NITROUS OXIDE-HALOTHANE ANAESTHESIA IN THE DOG

In dogs under nitrous oxide-halothane anaesthesia, ventriculararrhythmias were produced by intravenous injection of adrenalineand noradrenaline 2–3 µg/kg or isoprenaline 1µg/kg,and completely prevented by propranolol 0.3 mg/kg. Adrenalineor noradrenaline (20–30 µg/kg) produced slow rateventricular extrasystoles and ventricular bigeminy, withoutincrease in the rate of sinus rhythm. Doses of 100 to 150 µg/kgproduced ventricular tachycardia in all and ventricular fibrillationin some experiments. Increase in sinus rate always precededventricular tachycardia. Isoprenaline 10 µ/kg producedventricular tachycardia preceded by an increase in sinus rate.Very large doses (50 µg/kg) produced a greater increasein sinus rate, and later ventricular tachycardia and even ventricularfibrillation resulted in all the experiments. Dosages of catecholamineswhich did not produce any increase in the rate of sinus rhythmnever produced ventricular tachycardia or fibrillation.