Some physiological characteristics of the esophagogastric junction in the opossum.

Abstract

Abstract Bilateral cervical vagotomy did not change closure tension or abolish relaxation with swallowing in the lower esophageal sphincter of the opossum, studied by manometry in vivo. Field electrical stimulation of serial transverse muscle strips, 2 mm wide, cut from a zone spanning the opossum esophagogastric junction, distinguished three regions. Muscle distal to the junction contracted during the stimulus. Muscle at the junction relaxed during the stimulus. Muscle proximal to the junction contracted after the stimulus. Transitional responses occurred. All responses were sensitive to tetrodotoxin. Muscle from the junction showed a steeper length-tension curve than muscle from adjacent regions. A steep length-tension curve was correlated in space with stimulus-induced relaxation. Basal tension during stretch to 150% of resting length was not sensitive to tetrodotoxin. A fraction of sphincter closure tension and relaxation with swallows are independent of central vagal connections. Muscle of the esophagogastric junction differs from that of adjacent regions in showing a steeper length-tension curve and nerve-mediated stimulus relaxation. These characteristics seem to define the sphincter. The sphincter in the opossum is less than 1 cm long.