Uptake of Macromolecules by Enterocytes on Transposed and Isolated Piglet Small Intestine1

Previous work dealing with the internalization of macro- molecules by enterocytes of neonatal piglet small intestine showed that the enterocytes of the proximal gut exhibited closure (ceased internalizing fluorescent protein) before those of the middle gut, which, in turn, ex hibited closure before those of the distal gut. The rate of closure, however, could be manipulated by dietary regimen. The effect of digesta on closure as it relates to the position of the enterocyte in the digestive path was studied by either surgically transposing a portion of the ileum to the proximal third of the small intestine or isolating different regions of the small intestine from the direct digestive path. Transposition experiments illustrated that the neonatal piglet possesses a differentiated intestinal epithelium with regard to its capacity to internalize macromolecules. That is, enterocytes on ileum surgically transposed to the proximal intestine con tinued to internalize fluorescent protein after enterocytes on the proximal intestine on each side of the transposed ileum ceased. Upon isolation from the direct digestive pathway, enterocytes on intestinal segments from the proximal, middle, and distal thirds of the small intestine internalized fluorescent protein longer than comparable enterocytes remaining in the digestive path. It was concluded that digesta accelerates the rate of termi nation of the differentiated capacity of the neonatal piglet intestinal epithelium to internalize macromolecules. J. Nutr. 106: 419â€"427, 1976.