Site of horseadish peroxidase transport by the small intestine of the neonatal rat.

The absorption of horseradish peroxidase was estimated in 10-day-old rats by measuring plasma peroxidase levels following intraduodenal admininstration. Peak levels occurred 45 min after injection. Plasma peroxidase levels, 45 min after injection into five ligated segments along the small intestine, were significantly lower in rats with distal segments than in rats with proximal segments. This indicates that the proximal small intestine, including the duodenum, may play a significant role in nonantibody macromolecular transport as well as in immunoglobulin absorption.