The Site of Absorption of Co⁵⁸-Labeled Vitamin B₁₂ in Man : An Investigation Made by Intestinal Intubation with Polyethylene Glycol as a Marker Substance

Intestinal intubation was performed with a tri-bore tubing in ten subjects without signs of gastrointestinal disease. After administration of a test meal containing Co⁵⁸-labeled vitamin B₁₂ and with polyethylene glycol as a marker substance, samples of intestinal juice were collected from the upper, middle and anal thirds of the small intestine.

During the passage of the test dose from the upper to the middle third of the gut a modest, but significant, absorption of about 6 per cent was discovered. During the passage from the middle to the anal third of the intestine a considerably larger absorption took place, on an average of about 25 per cent of the oral dose.

These results agree entirely with those obtained from experiments performed in animals and with clinical observations in man after operations on the small intestine. The most outstanding feature was that, contrary to the generally accepted view, our study seems to indicate that in certain cases the absorption of B₁₂ begins far up in the jejunum. This seemed to be the case in 3 out of 9 experiments. The study throws no light on the cause of this.