RELEASE OF ADRENERGIC CATECHOLS AFTER THE ADMINISTRATION OF HEXAMETHONIUM BROMIDE

Abstract

The action of hexamethonium bromide in anaesthetized cats and dogs has been examined to determine whether the difficulty experienced in achieving satisfactory levels of hypotension by the use of this agent in clinical anaesthesia could be due to the action of hormones released reflexly from the adrenal medulla. The resistance to hexamethonium blockade of the junction between the preganglionic nerve fibres and the chromaffin cells of the adrenal medulla was found to be greater than that of the ganglionic synapses of the splanchnic vasoconstrictor nerves. It was found that the initial fall in the blood pressure induced by the intravenous injection of 2 mg/kg of hexamethonium bromide resulted in (i) a transitory increase in the respiratory rate, which coincided with a temporary and slight increase in the blood pressure, and (ii) a release of medullary hormones from the adrenal glands. These hormones produced an immediate and sustained rise in the blood pressure. The release of adrenergic catechols which followed the intravenous injection of 2 mg/kg of hexamethonium bromide would appear to depend on a diminution in the sensory discharge which results in inhibition of the centres of the medulla oblongata. The afferent nerves involved have been shown to be the nerves of Hering and the vagus nerves. It is assumed that the sensory receptors are the baroceptors of the cardio-aortic and carotid sinus areas. The efferent nerves were found to run in the splanchnic nerves and in the posterior thoracic sympathetic nerve chains.