Modulation of esophageal contractions by distension in vitro

Stimulation of the intrinsic nerves of the esophageal body leads to a twitch of the circular muscle after the end of the stimulation (the esophageal off-response), and the twitch spreads in the distal direction because of a latency gradient in the onset of the off-response between the proximal and the distal esophagus. We investigated the possibility that local input can modulate the basic off-response through intrinsic mechanisms and make it resemble more closely the sequential ring contractions that move boluses in the esophagus of intact animals (esophageal peristalsis). The esophagus up to the aortic arch and down to the gastroesophageal junction was removed from opossums and suspended in an organ bath containing 2 liters of Krebs solution at 36 degrees C. The mechanical activity of the esophagus was recorded by force transducers on the serosal surface of the esophagus 2, 4, and 6 cm above the LES. The intramural nerves of the proximal esophagus were stimulated by electrical pulses with and without distension of the esophagus by inflation of a luminal balloon. Balloon distension increased the latency of the off-response in the distal esophagus, thereby reducing the velocity at which the circular muscle contraction spread through the esophagus. In addition, balloon distension increased the amplitude and the duration of the esophageal circular muscle contraction (both off- and on-responses), and decreased the amplitude of the longitudinal muscle contraction (duration response) and LES response (relaxation response). Similar changes in the esophageal contraction responses were produced by radial stretch of an open preparation of the esophagus from which the mucosa had been removed.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for inhibition of opossum LES through intrinsic gastric nerves

We have studied the mechanical responses of the isolated opossum gastroesophageal junction to a variety of stimuli. Lower esophageal sphincter (LES) relaxations were readily produced by gastric stretch and by electrical stimulation of the intramural gastric nerves. Gastric stimulation also led in 60% of stimuli to a contraction of circular muscle (the off response) in the distal esophagus, but in less than 15% of stimuli to a contraction of longitudinal esophageal muscle (the duration response). Mechanical or electrical stimulation of the esophagus led to a mechanical response of the stomach (relaxation, contraction, or both) in 76% of stimuli. The LES relaxation produced by esophageal stimulation was not as long as that produced by gastric stimulation. Direct electrical stimulation of the esophageal or gastric muscle produced a ring contraction that spread readily across the gastroesophageal junction but did not produce a relaxation of the LES or a contraction of the longitudinal esophageal muscle. Thus intramural nervous pathways can coordinate the mechanical activity of the esophagus, LES, and stomach. LES relaxations may occur as part of intrinsic reflexes that mediate gastric accommodation to volume.