Abstract
The effect of orally administered cyanocobalamin and methylcobalamin on vitamin B_<12> storage in the rat liver and kidney was examined. Regardless of the dosage, the amount of vitamin B_<12> stored in the liver of rats fed the cyanocobalamin diet was about half of that in rats fed the methylcobalamin diets. In contrast, the amount of B_<12> accumulation in the kidney of rats fed the cyanocobalamin diet was higher than that in rats fed the methylcobalamin diet. Nevertheless, the proportions of four vitamin B_<12> analogues (hydroxo-, adenosyl-, cyano-, and methyl-cobalamin) stored in both organs were not affected by the type of cobalamin having different axial ligands in the diet. Moreover, the difference in the ligand type cobalamin in the diet did not affect the concentrations of circulating homocysteine and urinary methylmalonic acid. These results suggest that the storage capacity of vitamin B_<12> in the liver is determined by the type of the upper axial ligand of cobalamin in the diet.
