Intestinal permeability to polyethyleneglycol 600 in relation to macromolecular 'closure' in the neonatal pig

The intestinal permeability of different sized molecules in the neonatal pig was investigated. Piglets of varying age (0-168 h) were given a mixture of different sized polyethyleneglycols (414-942 dalton polyethyleneglycols) together with ovalbumin and bovine serum albumin by stomach tube, and the serum concentrations were determined two hours after feeding. Considerable amounts of ovalbumin and bovine serum albumin were found in the serum of animals up to 24 hours of age, whereas very little or none at all was found in sera from older animals. By contrast, an intestinal permeability barrier to polyethyleneglycols in the 414-942 dalton range was found not only in the older animals but in all pigs investigated, including the newborn, unsuckled. In addition, the permeability barrier to polyethyleneglycols was found in a pig which was starved to prevent macromolecular closure and, therefore, absorbed considerable amounts of bovine serum albumin and ovalbumin. These findings indicate that 414-942 dalton polyethyleneglycols cross the intestinal mucosa at different rates due to size regardless of age of the animals and regardless of whether the mucosa is permeable to protein or not. This suggests that low molecular weight molecules like 414-942 dalton polyethyleneglycols and macromolecules (proteins) cross the neonatal gut wall through different routes.