The metabolism of some folates in the rat

Abstract

1. A number of folates labelled with ¹⁴C were administered orally to rats, at various doses, and urinary, faecal and hepatic folates examined.2. 10-Formylpteroylmonoglutamic acid (10CHO—PGA) entered the folate pool very slowly, and is thought to be relatively ineffective in nutrition.3. 10-Formyl[2-¹⁴C]tetrahydrofolic acid (10CHO—[2-¹⁴C]THF) entered the folate pool very rapidly. 5-Methyl[2-¹⁴C]tetrahydrofolate (5CH₃—[2-¹⁴C]THF) was the major urinary folate.4. 5-Formyl[2-¹⁴C]tetrahydrofolic acid (5CHO—[2-¹⁴C]THF) entered the folate pool only to a small extent. 5CHO—[2-¹⁴C]THF, given intravenously, produced no urinary 5CH₃—[2-¹⁴C]THF in the first 6 h.5. 10-Methylidyne[2-¹⁴C]tetrahydrofolic acid was metabolized to an extent which was dependant on the dose. At doses of 3 and 30 μg/kg body-weight, 5CH₃—[2-¹⁴C]THF represented 5·4 and 20% respectively of urinary folates and for 10CHO—[2-¹⁴]PGA, the values were 16% of total urinary folates after the higher dose, and 78·5% after the lower dose.6. Results obtained for the metabolism of 5CH₃—THF varied depending on the position of the labelling: 5¹⁴CH₃–THF gave no labelled urinary folate, the methyl group being lost rapidly. When 5CH₃—[2-¹⁴C]THF was given, it appeared as the major urinary folate.7. Folates found in the liver after oral administration of labelled folates were identified by thin-layer chromatography; only folate monoglutamates were identified.