THE EFFECT OF IMMATURITY ON INTESTINAL HANDLING OF COW'S MILK PROTEINS

Abstract

To investigate postnatal maturational changes of gut barrier function, we used two small intestinal in vitro models. Microvillus membrane (MVM) preparations were used for studying membrane surface binding and the everted gut sac technique was used for studying mucous coat binding and uptake of 125I-labelled bovine serum albumin (125I-BSA) and betalactoglobulin (125I-BLG) in newborn, preweanling and adult rats. Surface binding of BSA and BLG to MVM was greater from newborn and preweanling rats, compared to adults (BSA, newborns: 2.74±0.53%; adults 1.08±0.17%, p<0.001). Binding however was weak and nonspecific. Contrary to surface binding, mucous coat binding of BSA and BLG to preweanling gut sacs was less than to adult ones, as was uptake (BSA binding: 0.94±0.30 vs 3.06±0.74 μg 125I-protein equivalents /mg mucosal protein, p<0.001; BSA uptake: 0.35±0.17 vs 0.71±0.20, p<0.01). Gut sac binding and uptake were closely correlated in adult and preweanling animals (r=0.76, p<0.001 for BSA; r=0.85, p<0.001 for BLG in preweanlings). These studies suggest that immature animals are binding more cow's milk proteins to their MVM, but that less protein is bound to the mucous coat and taken up by immature gut sacs. Differential handling, mucous coat and MVM binding of food proteins in immature animals may be controlled by mucus layer factors which act to protect the underlying MVM.