Effects of acute experimental esophagitis on mechanical properties of the lower esophageal sphincter.

The mechanical properties of the cat lower esophageal sphincter (LES) circular muscle were studied in untreated animals and in cats that had biopsy-proven esophagitis induced by 30-min perfusions of 0.1 N HCl 5 cm above the LES on four consecutive days. The location of the in vivo LES was identified by the pull-through method with a pressure measuring probe. Consecutive rings were cut from the LES and esophagus and tested in vitro. Force-length curves were obtained in standard Tyrode solution, in Tyrode solution with 140 mM KCl, and in Ca-free Tyrode solution with 5 mM ethylenediaminetetra-acetic acid to determine basal, total, and passive forces, respectively. The active force was measured as the difference between the total and passive forces, whereas the basal-active force was measured as the difference between the basal and passive forces. In the untreated animals, LES rings exhibited the steepest basal force-length curve and the highest active and total forces under maximal KCl stimulation. The passive force of the LES rings was equal to that of the esophageal body rings. Basal in vitro forces were significantly reduced in all acid-perfused animals, whereas the passive forces were not affected. Active and basal-active forces were also significantly reduced. The maximum active force developed by LES rings was reduced, whereas esophageal rings, four rings proximal to the ring corresponding to the high pressure point, were not affected. The reduction in LES active force was related to the intensity of histologic damage, whereas basal-active forces were uniformly reduced. This study shows that in vitro mechanical properties of the LES are affected by induction of esophagitis and suggests that the ability to develop tonus in the basal state is reduced by acid perfusion, even in animals in which the ability to develop active contraction in response to maximal KCl stimulation is preserved. The response to KCl is reduced only by more extensive histologic damage.