FOLIC-ACID, 5-METHYL-TETRAHYDROFOLATE AND 5-FORMYL-TETRAHYDROFOLATE EXHIBIT EQUIVALENT INTESTINAL-ABSORPTION, METABOLISM AND INVIVO KINETICS IN RATS

The intestinal absorption and in vivo kinetics of (6S)-[H-3]-5-methyl-tetrahydrofolate (5-methyl-H-4folate), (6S)-[H-3]-5-formyl-H-4folate and [H-3]folic acid were investigated to determine whether inherent differences exist in the overall bioavailability of these folates in rats. Adult rats (n = 9 per group) were given an intragastric dose of the appropriate folate (50 pmol/100 g body wt) in 50 mmol/L ascorbate (pH 7). Each compound underwent nearly complete absorption within 8 h, and there was no significant difference in the excretion kinetics in relation to the form of folate administered. A biphasic pattern of excretion was observed over the following 8 d. Both urine and feces were important excretory routes. The rapid phase of total isotopic excretion (urinary and fecal) exhibited a half time (t1/2) of 0.11-0.12 d, whereas the t1/2 of the slower phase was 13.4-15.9 d. isotopic distributions and the pattern of labeled folates in urine and tissues were similar regardless of the form administered. These results indicate that the bioavailability of orally administered folic acid, 5-methyl-H-4folate and 5-formyl-H-4folate is equivalent in rats under the conditions of this study.