The Development of Selectivity of Protein Absorption From the Intestine During Sucking in the Rat

Summary Preparations of purified rat albumin transferring, γ‐globulin, whole rat serum and rat milm whey, labeled with radioactive iodine, where administered intragastrically to suckling rats aged from 1 to 21 days. Absorption of the proteins was determined by measuring protein‐bound radioactivity in the suckling rats serum 4 hr. later. It was found that on the 1st and 3rd days after birth all three purified proteins were absorbed, but by the 7th day albumin absorption had ceased, and by the 21st day no proteins were absorbed. On the 7th and 14th days γ‐globulin absorption was greater than that of transferrin. The results with whole serum and whey showed that, with increasing age during suckling. Absorption ceased first with the albumin‐fractions, then with the α‐globlins and last of all with the β‐ and γ‐globulin fractions. It is concluded that the suckling rat shows a progressive increase with age in selectivity for absorption of proteins from the alimentary canal and that this is related to the net electric charge carried by the proteins.