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Further Studies on the Absorption of Vitamin B₁₂ Following Oral and Parenteral Administration^1,2,

Department of Biochemistry, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland

Vitamin B₁₂ was administered subcutaneously to groups of normal rats at dosages ranging from 10 to 0.31 µg. It was found that at the higher levels the recovery of this vitamin in the urine was almost quantitative. As the dosage decreased, the recovery became poorer. At low levels, no increase of microbiological activity over the basal excretion was observed. The data taken as a whole suggest that the tissues of the body retained about 1 or 2 µg of the vitamin per rat.

A large fraction of orally administered vitamin B₁₂ appeared in the feces; urinary excretion was very low, indicating poor absorption. Nevertheless, some absorption must have taken place, since oral feeding of large doses to dogs was followed not only by appearance of activity in the urine but by occurrence of demonstrable blood levels.

² The authors express their appreciation to Mrs. Shanley L. Davis for her faithful assistance in the microbiological assay of vitamin B₁₂.

Manuscript received 13 July 1951.