Vitamin B12Co-60 readily passes the placenta into fetal organs and nursing provides B12 from mother to pup. A record of its distribution.

The placenta is permeable to B(12)Co(60). Together with salts, sugar, amino acids, vitamins, and proteins, the B(12) is contributed to the growing embryos from the mother's body stores. At birth, the placenta contains a liberal amount of B(12), which the mother regains by ingestion of the placentas. Nursing draws a liberal amount of B(12)Co(60) from the mother's stores and contributes it to the body of the pups where it is absorbed and distributed in the various organs, much as noted when adult dogs are injected with B(12)Co(60). A redistribution is noted as the months pass; but the high values in the heart, liver, and gastric mucosa persist, and the brain usually shows a slow increase. Enterohepatic circulation of B(12) may involve bile and enteric content plus hepatic, gastric, and pancreatic epithelial secretion. This type of body recycling of radioactive B(12) is discussed but not proven. High values of B(12) in the heart, brain, gastric mucosa, and liver indicate that the vitamin is functionally active, not an inert fraction.