Evidence for a lower oesophageal sphincter in the guinea-pig

1. In vitro balloon pull-through experiments have been used to identify the guinea-pig lower oesophageal sphincter (LOS). 2. Histologically, the LOS forms a 1-2 mm ring of smooth muscle at the distal termination of the oesophagus, immediately adjacent to the gastric sling muscle. 3. Tetrodotoxin (10(-6) M) sensitive, guanethidine (10(-6) M) insensitive "on" relaxation of circular LOS muscle strips was evoked by electrical field stimulation (ES). 4. ES evoked atropine (10(-6) M) sensitive "on" contractions of gastric sling and fundus smooth muscle strips. 5. Following cessation of ES a partially atropine-sensitive "off" contraction was observed in all the smooth muscle strips. 6. The predominant response of the LOS to ES was relaxation.