Intestinal folate absorption. I. 5-Methyltetrahydrofolic acid.
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. These results indicate that 5-MTHF is not absorbed by the rat small intestine by a carrier-mediated system and suggest that 5-MTHF transfer most likely represents diffusion.
D000818:Animals; D001692:Biological Transport; D002850:Chromatography, Gel; D004058:Diffusion; D004386:Duodenum; D005492:Folic Acid / Q000378:metabolism*; D007082:Ileum; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000502:physiology*; D007583:Jejunum; D008297:Male; D051381:Rats; D012704:Serous Membrane / Q000378:metabolism; D014316:Tritium
D014316:Tritium; D005492:Folic Acid