Intestinal uptake and transmission of macromolecules into the blood in the young guinea pig.

The developmental changes in the ability of the small intestinal epithelium to take up and transfer into blood the macromolecules bovine serum albumin (BSA), bovine immunoglobulin G (BIgG), and fluorescein isothiocyanate-labeled dextran 70,000 (FITC-dextran) were studied in guinea pigs 0-14 days of age. In addition, in the same animals, the activities of the proteases cathepsin B and D within the intestinal mucosa were measured. Four hours after gavage feeding, 0-day-old guinea pigs showed an uptake of the markers into the enterocytes throughout the small intestine. In 2-day-old guinea pigs, the markers were only detected in the enterocytes in the distal part. All three macromolecules passed into the blood in these young animals. In 7-day-old guinea pigs, no epithelial marker uptake was observed, but low levels of BSA and FITC-dextran could still be detected in serum. Neither epithelial uptake nor transfer of the markers to the blood could be found in the animals that were 14 days of age. The activity of cathepsin B and D in the intestinal mucosa showed a tendency to increase with age, and for all ages the activity in the distal part was higher than in the proximal part. The results showed that the small intestine in guinea pigs at birth is capable of macromolecular uptake and transfer into the circulation. This ability decreased with age eventually leading to intestinal closure after 1 week. The histological findings implied that intestinal closure was a consequence of a replacement of fetal absorptive cells with adult cells lacking this ability.