Background/aims: The lower esophageal sphincter (LES) pressure in humans is asymmetric; the highest pressure and the most significant cholinergic contribution occurs toward the left. The basis of this asymmetry was examined using the cat as a model.
Methods: The LES pressure profile was determined using a manometry catheter with four ports oriented at right angles. The LES was dissected into right and left halves with the latter including a contribution from the oblique gastric sling fibers. Isometric tension responses were studied in vitro.
Results: In vivo, both the initial LES pressure (31.8 +/- 4.0 mm Hg) and the decrease (79.9% +/- 6.4%) after intravenous atropine (100 micrograms/kg) were greatest in the leftward direction. In vitro, both halves of the LES developed similar spontaneous tension, but the increase in tension to carbachol was twofold greater on the left than the right. Eserine increased and atropine decreased initial tension by 25%-30% in both. Strips from either side relaxed in response to electrical stimulation but the response was more complete in strips from the right, whereas sodium nitroprusside produced similar relaxation in both.
Conclusions: Regional differences in the LES pressure and its cholinergic component can be accounted for by differences in the in vitro properties of the LES muscle fiber groups.