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Intestinal absorption and concurrent chemical changes of methylcobalamin

  • Kunio Okuda
    Correspondence
    Reprint requests: Dr. Kunio Okuda, Professor of Medicine, Chiba University Hospital. Inohana, Chiba (280), Japan.
    Affiliations
    From the First Department of Medicine, Chiba University School of Medicine, Chiba, Japan

    From the Second Department of Medicine, Kurume University School of Medicine, Kurume, Japan
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  • Keisuke Yashima
    Affiliations
    From the First Department of Medicine, Chiba University School of Medicine, Chiba, Japan

    From the Second Department of Medicine, Kurume University School of Medicine, Kurume, Japan
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  • Tetsuro Kitazaki
    Affiliations
    From the First Department of Medicine, Chiba University School of Medicine, Chiba, Japan

    From the Second Department of Medicine, Kurume University School of Medicine, Kurume, Japan
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  • Isao Takara
    Affiliations
    From the First Department of Medicine, Chiba University School of Medicine, Chiba, Japan

    From the Second Department of Medicine, Kurume University School of Medicine, Kurume, Japan
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      Abstract

      Intestinal absorption of 14CH3- and/or 57Co-methylcobalamin (CH3-B12) was studied with regard to chemical changes. It was found that absorption of a physiologic dose of CH3-B12-57Co in the rat was the same as that of cyanocobalamin (CN-B12) in quantity and speed, but more radioactivity accumulated in liver after 8 hours, indicating a gradual conversion of CH3-B12 to hydroxocobalamin and cobamide coenzyme. Schilling test with CH3-B12-57Co yielded urinary excretion about Math Eq that with CN-B12-57Co, and similar changes of CH3-B12 in human body were suggested. In the rat, expiration of 14CO2 following oral administration of 14CH3-B12 was small, as contrasted by quick and massive evolution of 14CO2 when photolyzed 14CH3-B12 was given. With supraphysiologic doses, more than 60 per cent of 14C disappeared from the gastrointestinal tract in 2 to 3 hours, suggesting instability of free CH3-B12, and there was a distinct difference in tissue distribution between 14C and 57Co following administration of 14CH3-B12-57Co. It seems, therefore, that cleavage of -CH3 in vivo is different in mechanism from that in vitro or after photolysis. Paper chromatography of digested ileal mucosa obtained after oral administration of a small dose of CH3-B12-57Co, demonstrated unchanged CH3-B12 and some other cobamides. It is concluded that in the alimentary tract, free CH3-B12 is labile and loses CH3 progressively. However, in a physiologic situation where intrinsic factor is operative, CH3-B12 may be partially protected by it from such chemical changes.
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