Selective Absorption of Macromolecules into Intestinal Epithelium and Blood by Neonatal Mice

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Abstract
Selectivity of absorption of macromolecules in the neonate could occur: (A) in the lumen of the intestine (digested, therefore unavailable for absorption); (B) at the plasmalemma of the intestinal epithelium (not adsorbed, therefore not internalized); (C) beyond the plasmalemma of the intestinal epithelium (internalized and either trapped within the epithelial cell or undetected in blood because of its rapid catabolism). Using serology, it was determined that during the neonatal period (1 to 17 days of age) mice absorbed from their gut into their blood γ-globulin from a number of animal species. No albumins appeared in the blood during this time. This selective absorption pattern was not altered by blocking the reticuloendothelial system with colloidal carbon. However, when the intestinal epithelium from neonatal mice gavaged with fluorescent proteins was examined no such selectivity was demonstrated. Albumins and globulins alike were equally absorbed within the epithelial cell. Thus, it is likely that mammalian neonates are similar in that they nonselectively absorb, via pinocytosis, macromolecules into gut epithelium but differ with respect to the macromolecules found in the blood.