Folate-binding protein and the absorption of folic acid in the small intestine of the suckling rat.
The folate in milk is largely bound to high-affinity folate-binding protein (FBP). With an in vivo intestinal loop technique, we examined the absorption of folic acid bound to FBP (FA-FBP) in the small intestine of the suckling rat. In contrast to unbound folic acid (FA), FA-FBP is absorbed more avidly in the ileum than in the jejunum (p less than 0.025) and its absorption is not inhibited by 1 mmol sulfasalazine/L. Folate-binding activities in the mucosa of the proximal (duodenum and jejunum combined) and distal (ileum) small intestine were also examined and found to be 0.32 and 1.31 pmol/mg protein, respectively (p less than 0.001). A 6-h fast produced a 42% decrease in folate-binding activity in the distal small intestine (p less than 0.01) but did not change activity in the proximal portion. Collectively, these observations suggest that FA-FBP is absorbed by a mechanism that is distinct from that responsible for the absorption of FA and that absorption does not require prior dissociation of the vitamin-binding protein complex.
Mason
J B
JB
Section of Gastroenterology, University of Chicago, IL.
Selhub
J
J
D000818:Animals; D000833:Animals, Suckling / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism*; D007082:Ileum / Q000378:metabolism; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface; D014316:Tritium
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D014316:Tritium; D005492:Folic Acid