565 CONTRACTILITY OF THE DEVELOPING LOWER ESOPHAGEAL SPHINCTER IN THE KITTEN

Abstract

The lower esophageal sphincters (LES) of kittens aged 3 days, 1 week, 3 weeks, and 6 weeks were identified by a probe with a perfused side opening adjacent to a metal plug, and basal LESP was measured. A suture was placed under fluoroscopy at the LES. 1.75 mm wide rings were cut transversely from the LES region and studied in vitro. Force/length curves were obtained in standard tyrode solution, in tyrode with 140 mM KCL, and in calcium-free tyrode with 5 mM EDTA to determine basal, total and passive forces respectively. Active force was obtained as the difference between total and passive force. Circular smooth muscle thickness was determined in such age group from frozen sections. The forces generated were then normalized for the amount of muscle able to generate them to give stress or contractility of the muscle.

In the kitten, in vivo LESP, forces generated by LES rings in vitro, and thickness of the smooth muscle all increase throughout life. Contractility of the LES rises to a peak at 3 weeks and then declines. This increased contractility may be important in determining sphincter competence during infancy.