INTESTINAL ADAPTATION DURING LACTATION IN THE MOUSE .2. ALTERED INTESTINAL PROCESSING OF A DIETARY-PROTEIN

We previously demonstrated in lactating mice a six- to eightfold incre ase in the intestinal uptake of the dietary protein, ovalbumin (OVA), administered by gavage. In this study, we tested the possibility that alterations in intestinal morphology, transit time, reduced luminal pr oteolysis, and enhanced association with the intestinal surface might account for the increased uptake of the protein observed in lactating mice. We found that these animals had a significant increase in length , wet weight, and surface area of the small intestine. No change in th e number of Peyer's patches was noted. Intestinal transit was assessed by gavage administration of I-125-OVA and 10 mg OVA and localization of the peak of radioactivity 15, 30, and 60 min after feeding. Althoug h motility (distance traveled per unit time) was not different in lact ating and control mice at 15 and 30 min, the fraction of the small int estine traversed by the peak of radioactivity was less in lactating mi ce. Digestion of I-125-OVA administered by gavage with 10 mg unlabeled OVA was examined by trichloroacetic acid precipitation and gel permea tion of the resulting fragments. Lactating and control mice did not sh ow differences in digestion of I-125-OVA by either measurement. The as sociation of I-125-OVA with small intestinal segments, however, was en hanced in lactating mice, especially in the second and third segments of the small intestine. Thus several factors including an increase in length and surface area of the small intestine, prolonged contact of p rotein with the small intestinal absorptive surface, and enhanced asso ciation of the protein with the intestinal surface contribute to incre ased uptake. Neither differences in number of Peyer's patches nor in t he rate of digestion of OVA were found, making it unlikely that these variables contribute to the enhanced uptake of protein observed in lac tating mice.