In Vivo Plasma and Urine Folate Binding after Ingestion of 3H‐Folic Acid and 14C‐Methyl‐Folate

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Abstract
After simultaneous ingestion [by humans] of equivalent amounts of [3H]folic acid (3H-PteGlu) and [14C]N5-methyl-tetrahydrofolic acid (14C-CH3-H4PteGlu), progressive macromolecular binding of radiofolate in plasma was followed and appeared to be near maximal at 6 h. Bound radiofolate was predominantly of 14C-CH3H4PteGlu origin, and only at 24 h could 3H incorporation be demonstrated. The binder eluted with albumin from Sephadex DEAE-A50 columns. In urine a smaller bound radiofolate fraction, with approximately equal amounts of 3H and 14C, appeared after 5.5 h. Plasma chromatography showed radio-PteGlu (peak 1) to be rapidly converted to CH3-H4PteGlu (peak 2), with subsequent appearance of 2 further radiofolate peaks (peaks 3 and 4) of unknown nature. Urine showed similarly placed fractions, but their magnitude differed, and urinary peak 3 in particular was much more prominent than its plasma counterpart.

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