Formylation of folate as step in physiological folate absorption

Oral administration of folate analogues to rats is followed by a rise in plasma folate detectable only by micro-biological assay with Lactobacillus casei, suggesting methylation of folate during absorption. When using the everted rat gut technique with folate (PteGlu), dihydrofolate (H(2)PteGlu), or tetrahydrofolate (H(4)PteGlu) on the mucosal surface formyl folate (10-CHO-PteGlu, 10-CHO-H(4)PteGlu, 5-CHO-H(4)PteGlu) and methylfolate (5-CH(3)-H(4)PteGlu) are recovered from the serosal fluid. This indicates that absorption of PteGlu is followed by formylation and that the formyl group is further reduced to methyl, 5-CH(3)-H(4)PteGlu passing on to portal blood.