Identification of longitudinal muscle activity in opossum lower esophageal sphincter

The aim of this study was to characterize lower esophageal sphincter (LES) longitudinal muscle contraction during changes in LES pressure in opossums. LES pressure was used as a marker of LES circular muscle contraction. Longitudinal muscle contraction was measured by strain gauge transducers. For precise placement of the strain gauge on the LES, the high-pressure zone was identified using a manometric-laser illumination technique. Measurements were made during 1) spontaneous LES pressure fluctuations, 2) LES pressure changes induced by pharmacological agents, and 3) LES relaxation induced by vagal nerve stimulation. These studies show that 1) spontaneous LES pressure fluctuations correlated with spontaneous changes in LES longitudinal muscle contraction; 2) pharmacologically induced contraction and relaxation of LES pressure correlated with contraction and relaxation of LES longitudinal muscle, respectively; 3) a close temporal relationship existed between changes in LES longitudinal muscle contraction and LES pressure that occurred spontaneously or were induced pharmacologically; and 4) vagal stimulation caused LES longitudinal muscle contraction and LES pressure relaxation. We propose that LES longitudinal muscle may play a role in the modulation of intraluminal LES pressure.