Developmental characteristics of the lower esophageal sphincter in the kitten

Gastroesophageal reflux is a common event during infancy. Developmental factors may be responsible for incompetence of the lower esophageal sphincter (LES) in this age group. We used the cat as a model to evaluate in vivo and in vitro the mechanical factors responsible for LES pressure during infancy. We found that in vivo the kitten develops lower LES pressure than the adult cat. For in vitro studies consecutive rings 1.75 mm wide were obtained from the LES region of 3-day-, 1-wk-, 3-wk-, and 6-wk-old kittens and of adult animals. Force-length curves were obtained in standard Tyrode's solution, in Tyrode's solution with high KCl, and in calcium-free Tyrode's solution with ethylenediaminetetraacetic acid disodium salt to determine basal, total, and passive forces, respectively. Active force is given by the difference between total and passive force. The maximum active force generated was lowest in the 3-day-old kittens and increased with age, being highest in the adult cat. Stresses, obtained by normalizing forces for the amount of muscle available, were greater in the kitten than the adult. The ratio of muscle thickness to its inner radius is markedly reduced in the kitten. As intraluminal or LES pressure is given by the product of stress and thickness-to-radius ratio, this might explain why lower pressures are generated despite the higher stresses developed.