Influence of folate-binding protein from bovine milk on the absorption of folate in gastrointestinal tract of rat.

The absorption of [14C]pteroylglutamic acid (PteGlu) bound to the folate-binding protein of bovine milk was investigated in rat gastrointestinal tract in vivo and in situ. When bound [14C]PteGlu was given to rat intragastrically via oral intubation, a considerable amount of PteGlu was released from folate-binding protein under the acidic conditions in stomach, and it recombined with folate-binding protein in jejunum in vivo. Compared with free PteGlu, bound PteGlu was more gradually absorbed in small intestine, but finally the total amount of bound PteGlu absorbed was almost the same as that of free PteGlu. In all experiments in situ, bound PteGlu was only slightly absorbed in jejunum, where free PteGlu was rapidly absorbed under the same conditions. On the other hand, the absorption rates of the two forms of PteGlu were almost similar to each other in ileum. These results suggest that PteGlu bound to folate-binding protein is absorbed by a manner different from that of free PteGlu in rat gastrointestinal tract.