Evidence for inhibition of opossum LES through intrinsic gastric nerves

We have studied the mechanical responses of the isolated opossum gastroesophageal junction to a variety of stimuli. Lower esophageal sphincter (LES) relaxations were readily produced by gastric stretch and by electrical stimulation of the intramural gastric nerves. Gastric stimulation also led in 60% of stimuli to a contraction of circular muscle (the off response) in the distal esophagus, but in less than 15% of stimuli to a contraction of longitudinal esophageal muscle (the duration response). Mechanical or electrical stimulation of the esophagus led to a mechanical response of the stomach (relaxation, contraction, or both) in 76% of stimuli. The LES relaxation produced by esophageal stimulation was not as long as that produced by gastric stimulation. Direct electrical stimulation of the esophageal or gastric muscle produced a ring contraction that spread readily across the gastroesophageal junction but did not produce a relaxation of the LES or a contraction of the longitudinal esophageal muscle. Thus intramural nervous pathways can coordinate the mechanical activity of the esophagus, LES, and stomach. LES relaxations may occur as part of intrinsic reflexes that mediate gastric accommodation to volume.