MECHANISM FOR THE REDUCTION IN PULMONARY RESISTANCE INDUCED BY HALOTHANE

¹ Department of Pharmacology, School of Medicine, University of Pennsylvania, Phildelphia, Pennsylvania

The mechanism for the bronchodilator properties of halothane was investigated in the dog. In 18 dogs without premedication, administration of 0.5 to 3.0% halothane in oxygen caused a reduction in pulmonary resistance and increase in compliance. Increase of halothane arterial blood levels from 15 to 30 mg/100 ml caused a decrease in pulmonary resistance of 40%, a rise in compliance of 24% and a decrease of respiratory minute volume of 37%. Changes in pulmonary resistance could still be elicited after the following procedures: bilateral acute or chronic upper thoracic sympathectomy, bilateral adrenalectomy, intravenous administration of hexamethonium, reserpine, guanethidine or bretylium. The only drug which eliminated the response was compound MJ 1999 (dl-4-(2-isopropylamino-1-hydroxethyl)-methanesulfonanilide HCl), a beta adrenergic blocking agent. We conclude that halothane stimulates the beta receptors in the airway.