Abstract
When Co5’-vitamin B12 is fed by stomach tube to neonatal rats the vitamin is present in the wall of the lower jejunum and upper ileum within 30 min. The vitamin appears in the carcass 2 hr after feeding and, by 5 hr, transport from the gut to the carcass approaches a maximum rate. Transport of the vitamin does not require the presence of either gastric intrinsic factor or the vitamin B12-binding protein in mother’s milk. The intestinal transport of the vitamin appears to involve a saturable intermediate. Orally administered vitamin Bl2 derivatives interfere with transport. The limited capacity of the transport mechanism contrasts with the ability of the intestinal epithelium to ingest large amounts of the vitamin by pinocytosis. The vitamin which is still present in the intestinal wall after 24 hr, by which time transport to the carcass has ceased, appears to return to the intestinal lumen.
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