Plasma catecholamines following low and high doses of ouabain in anesthetized dogs with or without cervical vagotomy

Circulating catecholamine (CA) levels in the aortic blood did not change significantly in anesthetized dogs during a period of 60 min following the rapid intravenous injection of ouabain at a dose of 10 microgram/kg, but they did increase significantly after administration of a dose of 75 microgram/kg. After bilateral cervical vagotomy, the high dose of ouabain caused a greater and earlier elevation in circulating CA levels than in intact animals along with an increased cardiac index and a lower peripheral resistance. These findings suggest the existence of a vagal inhibitory mechanism upon liberation of CA following the administration of ouabain. Although ventricular arrhythmias did occur before the increase in circulating CA, preinjection CA levels were significantly higher in animals presenting ventricular fibrillation, suggesting that a high background adrenergic tone facilitates the production of ventricular arrhythmias by ouabain. Moreover, ventricular tachycardia occurred earlier in vagotomized dogs, in which the immediate elevation of circulating CA could have been a precipitating factor for this type of arrhythmia.