The Absorption of Cyanocobalamin (Vitamin B12) from the gastrointestinal tract of dogs

Abstract

In the post-absorptive state, plasma vitamin B₁₂ activity of dogs is the same in portal and peripheral blood plasma, but portal plasma contains greater amounts of activity than does peripheral plasma during active absorption of the vitamin from the intestinal tract. Crystalline vitamin B₁₂ placed in ligated segments of the duodenum or in the unligated duodenum of dogs results in the rapid appearance of vitamin B₁₂ activity in the plasma of portal and peripheral blood. During absorption, small but definite amounts of vitamin activity also appear in the urine. In dogs subjected to operation but administered saline in place of vitamin B₁₂, plasma and urine activity remained constant. The plasma vitamin B₁₂ activity of dogs with stomachs ligated at the duodenal cap remained essentially constant following the administration of vitamin. The major portion of vitamin B₁₂ administered by intravenous injection, in an amount approximately that found in plasma during oral absorption, results in a rapid elimination of the vitamin in the urine. These data are discussed in relation to the problem of vitamin B₁₂ absorption in man and animals.