The Microbiological Activity of Vitamin B12 in the Urine of Normal Rats Following the Oral and Subcutaneous Administration of this Vitamin

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Abstract
Vitamin B12 was given to a series of rats both by the oral and subcutaneous routes. Vitamin B12 activity was found to be absent in the urine of animals receiving B12 orally until a dosage of at least 270 µg/300 gm rat was reached. At this or a higher level, only a small fraction of the administered vitamin appeared in the urine. The administration of crystalline vitamin B12 to rats by the subcutaneous route caused the appearance of the microbiological activity of this vitamin in the urine in amounts essentially equal to the amount injected. Since it has been demonstrated that rats can absorb and utilize vitamin B12 for normal physiological functions, and since this species of animal, like man, cannot excrete this vitamin following oral administration, the absence of vitamin B12 activity in human urine cannot be taken as evidence that the vitamin is not absorbed or utilized by man.

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