EFFECTS OF SOME AUTONOMIC DRUGS ON CIRCULAR ESOPHAGEAL SMOOTH MUSCLE

¹ Department of Internal Medicine, University of Iowa, Iowa City, Iowa and Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada

Strips from the lowest centimeter of the cat esophagus were mounted to record tension and electrical activity in the circular muscle. There were no spontaneous contractions. Slow waves and spike bursts were absent in resting tissue but occurred during drug-induced activity. Cholinergic drugs produced contractions. Maximal responses to acetylcholine were less than those to methacholine and carbachol. Norepinephrine produced contractions opposed by tolazoline but not by propranolol. Contractile responses to the cholinergic drugs and to norepinephrine were opposed by atropine but were not altered by nicotine or hexamethonium. Responses to the four stimulating drugs declined slowly with time and tachyphylaxis was not apparent. Isoproterenol had no stimulating effect but depressed the contractile responses to cholinergic drugs. The degree of depression was dose-related. The effect was opposed by propranolol. Similar depression could be shown from norepinephrine and epinephrine in the presence of tolazoline. Thus, adrenergic alpha receptors in this tissue are excitatory and beta receptors inhibitory. Cholinergic drugs are excitatory. Relaxation of the lower esophageal sphincter, if mediated through adrenergic nerves, is a response to the stimulation of adrenergic beta receptors.

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