Intestinal absorption of the monoglutamate form of the principal dietary and circulating folate compound, 5-methyltetrahydrofolic acid (5-MTHF), was studied in the rat utilizing a synthetic highly purified radiolabeled diastereoisomer. Chromatography confirmed that the compound was not altered after transfer from the mucosa to the serosa. Accumulation against a concentration gradient was not observed in duodenal, jejunal, or ileal segments at 5-MTHF concentration from 0.5 to 500 nmoles/liter. Unidirectional transmural flux determination also did not indicate a significant net flux. Mucosal to serosal transfer of 5-MTHF was similar in all segments of the intestine and increased in a linear fashion with increased initial mucosal concentrations. Further, no alteration in 5-MTHF transfer was found when studied in the presence of metabolic inhibitors or folate compounds.
Williamson Strum, Peter F. Nixon, Joseph B. Bertino, Henry J. Binder