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Urinary Riboflavin Metabolites in the Rat^1,2,

Department of Nutrition, Letterman Army Institute of Research, Presidio of San Francisco, California 94129

Male rats were fed a riboflavin-deficient diet for 25 days and then fed [2-¹⁴C]riboflavin to replete their riboflavin pool(s). During a second depletion period, urine and feces were collected and ¹⁴C excretion monitored. The urine was chromatographed on R-15 resorcinol resin and ¹⁴C was measured in all fractions. The ¹⁴C compounds in the individual fractions were shown to be different by thin layer chromatography. The amount of ¹⁴C recovered as riboflavin increased after acid hydrolysis of the urine indicating the presence of riboflavin in conjugated forms. All R-15 fractions were found to support growth in a microbiological (L. casei) assay for riboflavin. This suggested that other derivatives, in addition to riboflavin and flavin nucleotides, are biologically active. However, the conjugated compounds were apparently less active, since acid hydrolysis of the urine enhanced its growth-promoting ability of L. casei. One ¹⁴C metabolite was identified as urea, thus providing evidence for degradation of the riboflavin molecule. This study has shown that the metabolic fates of riboflavin in the rat include conjugation and extensive degradation.

KEY WORDS: • riboflavin • riboflavin metabolites • rats

¹ The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.

² In conducting the research described in this report, the investigators adhered to the "Guide for Laboratory Animal Facilities and Care" as promulgated by the committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, National Academy of Sciences—National Research Council.

Manuscript received 6 February 1976.