Prolonged Catecholamine-Dependent Cardioaccelerator Action of Bretylium

Summary

Intravenous injection of 10 mg/kg of bretylium produced a sustained elevation of the heart rate in ganglioplegic dogs and in vagotomized spinal dogs and did not have this effect in reserpinized ganglioplegic dogs. At any time after bretylium injection the elevated heart rate could be reduced to the control level by injection of the beta adrenergic receptor-blocking agent, propranolol. The urinary norepinephrine output increased strikingly immediately after bretylium injection and then decreased to control levels, whereas the epinephrine output in the urine was not increased. On the basis of these results the tachycardia throughout the experiments could be attributed largely or entirely to the action of norepinephrine despite the inactivation of the cardioaccelerator pathway.