Intestinal permeability to large particles in normal and protein-deficient adult rats

Intestinal absorption of ferritin and virus particles was assessed in control and protein-deficient rats using light and electron microscopic procedures. Rats weighing 100 to 130 grams were divided into two groups and fed either a 0.5% of 18% lactalbumin diet. At monthly intervals following diet initiation, three rats from each group were administered ferritin (MW-650,000) or adenovirus Type 5 (MW is greater than 1,000,000) via ligated jejunal loops either 15 or 30 minutes prior to loop excision and processing for electron microscopy. Morphological evaluation of jejunal tissues revealed that both control and protein-deficient rats absorbed ferritin and virus particles via pinocytosis and in both situations the exogenous particles were believed to be present in lysosmal bodies of typical absorptive cells. Neither ferritin molecules nor virus particles were identified elsewhere in the jejunal mucosa of control rats. Rats deprived of sufficient dietary protein for four months or longer, however, demonstrated exogenous tracer materials in intercellular spaces of the epithelium and lamina propria. Since these severely protein-deprived rats also demonstrated deterioration of apical intercellular junctions, the possibility exists that large particles moved directly between cells of the epithelial lining and subsequently into underlying connective tissue and vascular compartments for conveyance (as antigens) to other body regions.