Mechanism of stretch-activated excitatory and inhibitory responses in the lower esophageal sphincter.

We recently found that an orally directed stretch of the esophagus activates a neurally mediated relaxation of the lower esophageal sphincter (LES). Goals of our study were to characterize the neural mechanisms responsible for axial and transverse stretch-activated responses in the LES. LES pressure was monitored in anesthetized and artificially ventilated mice. Sutures were placed in the esophagus to exert graded stretch in the longitudinal and transverse directions. Effects of bilateral vagotomy and pharmacological agents on the stretch-activated LES responses were investigated. The relationship between vagally stimulated axial stretch and LES relaxation was also studied. Stretch in the longitudinal and transverse directions caused a dose-dependent LES relaxation and contraction, respectively, that were not affected by bilateral vagotomy and sympathectomy but were blocked by tetrodotoxin. In bilateral vagotomized animals, hexamethonium, atropine, pyridoxalphosphate-6-azophenyl-2',4' disulfonic acid (PPADS), and ondansetron did not block the stretch-activated LES relaxation and contraction. Axial stretch-activated LES relaxation was blocked by nitric oxide inhibitor and transverse stretch-activated LES contraction was blocked by a combination of atropine and substance P antagonist. Electrical stimulation of the vagus nerve induced LES relaxation and axial stretch on the LES, both of which were blocked by rocuronium. Axial and transverse stretch-activated LES relaxation and contraction were present in the W/W(v) mice that lack interstitial cells of Cajal (ICC). Stretch-activated LES relaxation and contraction are mediated through mechanosensitive neurons located in the myenteric plexus, which involves neither synaptic transmission nor ICC.