Degradation of radioactively labelled protein in the small intestine of the suckling rat.

The absorption of 125I-labelled bovine IgG, after oral and intraluminal administration to young rats, has been followed by gel filtration and quantitatively by TCA precipitation. After intraluminal administration of the radioactive dose into the proximal small intestine most of the absorbed dose could be accounted for in a protein-bound form and the bulk of this radioactivity corresponded to native protein. Catabolism of the standard dose was far more efficient in the ileal regions of the small intestine, only 10% of the absorbed dose was transmitted as intact protein and large degradation products. Investigations on the attachment and release of labelled proteins from different sections of the small intestine of the young rat have also been recorded.