A long-term study of the excretion of folate and pterins in a human subject after ingestion of 14C folic acid, with observations on the effect of diphenylhydantoin administration.

After the administration of 2-14C folic acid to a human volunteer, urinary and fecal radioactivity, as well as urinary excretion of folate (Lactobacillus casei assay) and biopterin-like material (Crithidia fasciculata assay) were determined at intervals over a 129 day period of observation. From two 24 h urine samples erythroneopterin, bioterin, threoneopterin pterin, isoxanthopterin, and xanthopterin were isolated by chromatographic procedures, quantitated, and their specific activities were determined. The effect on the pattern of elimination of urinary radioactivity and biological activity resulting from the administration of diphenylhydantoin was studied on two occasions. Urinary radioactivity plots suggest the decay of two forms of folates with markedly different biological half lives. One short-lived (t 1/2 approximately 31.5 hr), corresponding to newly absorbed folate, and one long-lived (t 1/2 approximately 100 day) thought to represent the decay of body pools. Diphenylhydantoin does not alter the rate of elimination of the long-lived component but may accelerate losses of newly absorbed folate. The analysis of pterins does not support the hypothesis that diphenylhydantoin increases the breakdown of folates to pterins.