Intestinal absorption of intact proteins in normal and protein-deficient rats

Abstract

Intestinal absorption of macromolecules was assessed in control and protein-deficient rats using serological and morphological procedures. Animals weighing approximately 120 g were divided into two groups and given either a 0.5% or an 18% lactalbumin diet. At monthly intervals following diet initiation, eight animals from each group were examined for their capacity to absorb proteins from the small intestine. Five of the eight animals in each group received an oral dose of bovine serum albumin (BSA) 4 hr prior to blood collection. The remaining three animals were administered horseradish peroxidase via ligated jejunal loops before loop excision and processing for electron microscopy. Immunoelectroosmophoresis of sera revealed that, whereas both control and protein-deficient rats absorbed measurable quantities of BSA, protein deficiency promoted an increase in transport. Morphological evaluation of jejunal tissue from protein-deficient rats suggested initial increase in pinocytotic activity with eventual deterioration of apical junctions and movement of protein molecules directly between cells. The physiological significance of these findings is unknown, but the possibility exists that the animals may produce antibodies to the circulating foreign proteins with resultant anaphylaxis or deposition of antigen-antibody complexes in various body tissues.