In Vivo Transport of Water and Electrolytes in the Infant Rat Small Intestine

Abstract

In humans (1) and rats (2, 3), several aspects of gastrointestinal function appear to have characteristic developmental patterns. Little is known of the developmental changes in transport of water and electrolytes in the small intestine. Although the basic qualities of the transport mechanisms may not change during development, quantitative differences in transport of water and electrolytes may exist between infant and older animals. The present study was designed to determine if the in vivo transport of water, sodium, chloride, bicarbonate and potassium were quantitatively different in the jejunum and the ileum of 2-, 3and 8-week-old rats.Methods and materials. Male albino rats were obtained from mothers purchased from Biolabs. The post-weaning and the mother rats were fed a regular laboratory diet. The rats were studied at 2 weeks (14-15 days), 3 weeks (21-22 days) and 8 weeks (56 days) of age. The details of the methods used for the studies have been described before (4). After anesthesia with a mixture of urethanephenobarbital, the abdominal cavity was opened and approximately 15 cm segments of the jejunum, distal to the ligament of Treitz, and of the ileum, proximal to the ileocecal junction, were rinsed with an isotonic sodium chloride solution and cannulated. The intestine was ligated proximal and distal to the cannulated segments and placed back into the abdominal cavity. The temperature of the peritoneum was maintained at 36"-37" during the study period. The cannulated segments were perfused with solutions containing per liter: 120 mmoles of sodium chloride, 5 mmoles of potassium chloride, 25 mmoles of sodium bicarbonate, 100 pmoles of phenol red, and 25 mmoles of mannitol (-G solution), or an identical so-

Maturation of the Small Intestine: Absorption of L-Valine in Rats

“…The reason for this decline is again not understood, but cannot be explained on the basis of major differences in mucosal surface at the 3 age periods. The greater diffusion during suckling could be related to the general tendency of the permeability of the small intestinal mucosa to water, and electrolytes, including calcium to decrease with increasing age (13,14,15).…”