REGIONAL VARIATIONS IN RESPONSE OF CAT ESOPHAGEAL MUSCLE TO STIMULATION WITH DRUGS

¹ Gastroenterology Research Laboratory, Department of Internal Medicine, Univercity of Iowa, Iowa City, Iowa

We sought to explain differences in the regional responses of the esophagus to swallowing in terms of qualitative and quantitative differences in responses to drugs. Isometric contractions of muscle strips in vitro, in response to acetylcholine, carbachol, methacholine and norepinephrine, in concentrations from 10^-8 to 10^-5 g/ml, were measured to determine dose-response curves to these four drugs. Transverse strips of esophageal wall at various levels of the distal 12 cm of the cat esophagus were compared. There were no qualitative differences between responses of strips from the distal and midesophagus. The most proximal strips, from 10 to 12 cm above the phrenoesophageal ligament, exerted less tension than more distal strips at equal concentrations of all four drugs. These results fail to demonstrate a qualitative difference between sphincteric and nonsphincteric muscle. The diminished responsiveness of the most proximal level indicates that striated muscle, which predominates over smooth muscle at this level, is not stimulated under these conditions.