The effect of a histidine-excess diet on the hepatic folylpolyglutamate pattern in rat was studied using high-performance liquid chromatography with electrochemical detection. A highly sensitive method for the separation and quantitation of tetrahydrofolylpoyglutamate (H_4PteGlu_n) and their 5-methyl derivatives (CH_3H_4PteGlu_n) of different chain lengths (n=1〜6) was developed .These compounds were separated using a Cosmosil 5-Phenyl column with 50mM potassium dihydrogen phosphate, pH 2.2, containing 0.05M disodium EDTA and 1% methanol at a flow-rate of 1.5ml/min, and an electrochemical detector (at a potential of +350 mV versus the Ag/AgCl electrode). The detection limits at a signal-to-noise ratio of 3 for H_4PteGlu_n and CH_3H_4PteGlu_n series (n=1〜6) were 1〜10 and 10〜15 pmol, respectively. Rats were fed ad libitum 9.7% casein diets with 0.6% methionine (controls) or the basel diets supplemented with 3.5% histidine (His-rats). The liver weight of His-rats was 50% higher than controls. Hepatic methyltetrahydropteroylpentaglutamate (CH_3H_4PteGlu_5), and tetrahydropteroylmonoglutamate (H_4PteGlu) concentrations in His-rats was 5.7-and 2-fold higher than controls, respectively. The H_4PteGlu_5 concentration in His-rats was 74% lower than controls. Considering the homeostasis of folate cofactors in tissues, these results suggest that the hepatic regenaration systems of H_4PteGlu_5 in His-rats might be repressed and an apparent methylfolate trap might be attained rather on a pteroylpentaglutamate level than a monoglutamate level and, that the activity for catabolizing the excess histidine might exceed the regenerating activity for folate cofactors.
Twelve healthy adult men (aged 20-23) were administered a multivitamin preparation containing 13 or 26 μg of vitamin B_<12> (cyanocobalamin) every day for 7 days, and examined for changes in the plasma concentration and urinary excretion of vitamin B_<12>. 1) The daily, oral administration of 13 μg of vitamin B_<12> for 7 days caused practically no changes in the plasma vitamin B_<12> concentration. 2) The daily, oral administration of 26 μg of vitamin B_<12> for 7 days caused a tendency to slight elevation of plasma vitamin B_<12> concentration throughout the administration period. 3) Vitamin B_<12> was not detected in the urine of any subject before the administration of the multivitamin preparation but definitely detected in the urine of 2 of the 4 subjects administered 26 μg/day of the vitamin on days 5-7 of administration.