Variability of Pressure and Myoelectrical Activity Recorded from the Lower Esophageal Sphincter of Fasted Conscious Opossums

The opossum has served as an important model for studies of lower esophageal sphincter (LES) function. Previous investigations, however, have been confined to studies in anesthetized animals. Our aim in this study was to record LES pressure and electrical activity concurrently from conscious opossums. In four animals, we performed a cervical esophagostomy and implanted bipolar electrodes on the abdominal esophagus, LES, gastric antrum and duodenum. Beginning several weeks after surgery, 15 to 20 recording sessions, each lasting 4–6 hr, were obtained in each animal. Intraluminal pressure from the gastric antrum, LES and esophageal body was recorded by a manometric assembly that incorporated a sleeve device, while myoelectric activity from comparable sites was recorded via the implanted electrodes. In fasted conscious animals, interdigestive migratory myoelectric complexes (MMC’s) were readily recorded from the stomach and duodenum. These MMC’s had a cycle length of 86±2.9 (SE) min. The LES exhibited cyclic changes in its intraluminal pressure and myoelectrical activity that occurred in synchrony with the gastric MMC cycle. Basal LES pressure (24.1±2.1 mmHg) was lowest during phase I of the gastric MMC cycle and reached a maximal value (29.5±1.4 mmHg) during phase III of the gastric MMC. Phasic LES contractions began to appear during phase II of the gastric MMC, became pronounced during phase III and disappeared during phase I.