Abstract
Varying dosages of ^57Co-labeled methylcobalamin were injected to rats by subcutaneous, intramuscular and intravenous routes and the distribution of radioactivity was measured and compared with those for ^57Co-labeled cyanocobalamin and hydroxocobalamin. The urinary excretion was also determined in comparison with the two common analogues. It was found that methylcobalamin behaved somewhat like hydroxocobalamin with respect to tissue retention and excretion via the kidney. However, if given in large doses, it behaved more like cyanocobalamin in blood. These data seem to suggest a gradual conversion of methylcobalamin to hydroxocobalamin or coenzyme forms in vivo.
