The selective uptake and transmission of proteins to the circulation from the small intestine of the suckling rat.

The relative concentration of various immunoglobulins attain in the sera of 14-day-old rats have been compared 4 h after their oral and intraluminal administration. The circulatory concentration of these proteins attained higher values when they were administered into the isolated proximal small intestina than when they were administered into the distal small intestine. Selective uptake of proteins was shown to predominate in the proximal small intestine.