Disaccharide feedings enhance rat jejunal macromolecular absorption.

Disaccharide feedings to post-weaning rats alters their jejunal barrier to macromolecular absorption. Penetration of horseradish peroxidase (HRP) across the jejunum was enhanced after short-term high concentration gavage (30 g . kg-1 . day-1) of lactose that produces weight loss, osmotic diarrhea, and jejunal mucosal damage. HRP absorption was also increased by longer term feedings of lower levels of disaccharide that did not produce body weight alterations, diarrhea, or cell damage. Rats without diarrhea and gavaged with 7.5 g . kg-1 . day-1 of either lactose or maltose showed an increase in lumen to blood HRP absorption after 21 days of feedings. Also, lactose or maltose in the solid food diet at 30 g . kg-1 . day-1 for 21 days did not lead to diarrhea but produced an increase in jejunal lumen to blood HRP absorption. Rats having no diarrhea and receiving 15 g . kg-1 . day-1 of lactose or maltose in the drinking water for 21 days, showed an increase in jejunal HRP absorption. When rats were fed either lactose or maltose for 21 days glucose absorption became totally dependent upon the sugar concentration in the perfusion medium. The kinetics of this glucose absorption are compatible with a decrease in the "unstirred" layer. Disaccharide-induced HRP absorption may be mediated by transport from endocytotic vesicles across the jejunal epithelium.