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Folic Acid, 5-Methyl-Tetrahydrofolate and 5-Formyl-Tetrahydrofolate Exhibit Equivalent Intestinal Absorption, Metabolism and in Vivo Kinetics in Rats^1,2,3,

Food Science and Human Nutrition Department, University of Florida, Gainesville, FL 32611-0370

The intestinal absorption and in vivo kinetics of (6S)-[³H]-5-methyl-tetrahydrofolate (5-methyl-H₄folate), (6S)-[³H]-5-formyl-H₄folate and [³H]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 (t) of 0.11–0.12 d, whereas the t 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-H₄folate and 5-formyl-H₄folate is equivalent in rats under the conditions of this study.

KEY WORDS: • folate • kinetics • rats • absorption • bioavailability

¹ Presented in part at the 1991 Annual Meeting of the Federation of American Societies for Experimental Biology, Atlanta, GA [Bhandari, S. D. & Gregory, J. F. (1991) Tritiated folic acid, 5-methyl-tetrahydrofolate, and 5-formyl-tetrahydrofolate exhibit equivalent absorption and in vivo kinetics in rats. FASEB J. 5: A587 (abs.)].

² Supported by Grant #88-37200-3620 from the U.S. Department of Agriculture Competitive Research Grants Program.

³ Florida Agricultural Experiment Station Journal Series Number R-02178.

⁴ To whom correspondence should be addressed.

Manuscript received 3 February 1992. Revision accepted 18 May 1992.