Abstract
The stability of the methyl group attached to cobalt atom of methylcobalamin (CH_3-B_<12>), and hence the structural integrity of CH_3-B_<12> were studied in rats using ^<14>CH_3-B_<12> and CH_3-^<57>Co-B_<12> in vitro as well as in vivo. CH_3-B_<12> was relatively stable in the intestinal canal, and the radioactivity in the mucosa was mostly CH_3-B_<12> in the absorptive phase. When incubated with whole blood, the methyl group was not detached. Following parenteral injection of ^<14>CH_3-B_<12>, part of it was excreted in urine unchanged, and practically no release of methyl group was noted during filtration through the kidney. During incubation with liver homogenate, certain portion of the CH_3-B_<12> lost the methyl group but the reaction did not proceed beyond it. These data indicate that a good portion of oral CH_3-B_<12> is absorbed as such, and the compound is relatively stable in tissues, losing the methyl group gradually.
