Background/Aim: 

Recent studies show that an orally directed axial stretch on the lower esophageal sphincter (LES) induces LES relaxation. Electrical stimulation of vagus nerve causes contraction of the circular and the longitudinal muscles (LM) of the esophagus and LES relaxation in mice. We hypothesized that LM contraction induced axial stretch on the LES is the cause of LES relaxation.

Methods: 

Effects of rocuronium (a blocker of skeletal muscle contraction) on the vagally stimulated LES relaxation was studies in mice. Through a midline laprotomy, sutures were placed though the esophagus (just above the LES) and brought out through the mouth to exert axial stretch on LES. The LES displacement was measured with two piezo-electric crystals. The LES pressure was monitored with a 2F solid-state transducer placed in the LES. A second solid-state transducer placed in esophagus recorded esophageal contraction. Following bilateral cervical vagotomy, peripheral end of one of the vagus nerve was electrically stimulation.

Results: 

Axial stretch with 8 g weight induces maximum LES relaxation, which was reduced by 0.2 mg/kg rocuronium (from 95±12 to 73±14 %, P=0.04), Cranial LES displacement was unaltered (0.75±0.19 vs 0.68±0.25 mm, P=NS). Vagal stimulation induces frequency dependent LES relaxation and displacement of LES with a maximal response observed at 15 Hz. LES displacement (0.42±0.07 vs 0.03±0.004 mm, P<0.01), LES relaxation (95±4 vs 28±7%, P<0.05) and esophageal contraction (53.6±6.4 vs 18.3±16.1 mmHg) were almost abolished after 0.2mg/kg rocuronium.

Conclusion: 

Our data support the hypothesis that longitudinal muscle contraction related axial stretch on the LES is the cause of vagally stimulated LES relaxation.