Effect of cow's milk on jejunal mucosal macromolecular barrier in suckling guinea pigs.

The assumption that fresh cow's milk may have a direct effect on jejunal mucosal macromolecular permeability was tested in 14-day-old suckling guinea pigs, by in situ luminal perfusion of a proximal jejunal segment with horseradish peroxidase administered either in 0.9% NaCl or in cow's milk. For positive control, a group of guinea pigs previously sensitized to beta-lactoglobulin was similarly perfused with horseradish peroxidase in 0.9% NaCl or in cow's milk at 14 days of age. A segment of the wall of the perfused jejunal loop was processed for peroxidase staining and for examination of the extent and routes of macromolecular absorption by light and electron microscopy. Mucosal exposure to cow's milk was associated with penetration of tracer material across the jejunal epithelium only in the lactoglobulin-sensitized guinea pigs. In guinea pigs with a first-time exposure to cow's milk, no entry of tracer material beyond the brush border surface of the enterocytes was seen. Thus, whereas we could observe absorption of bystander antigens during antigenic challenge of the mucosa in sensitized animals, we found no evidence of a presumptive "permeability factor" in cow's milk that can disrupt the mucosal macromolecular barrier by an acute direct action.