Placental Transfer and Biological Half-life of Radioactive Vit. B12 in the Dog.

Abstract

Placental transfer of radioactive vitamin B12 in the dog following pregestational administration, was found in the entire litter to be 20% of the residual radioactive vitamin in the bitch at time of delivery. Because the proportional distribution of radioactive B12 among major organs of the mother and pups was found to be similar, it was possible to calculate placental transfer from this characteristic as well as by postpartum "calibration" of the hepatic radioactivity in pups. Biological half-life of the radioactive B12 averaged 2 months in pups and bitch during the postpartum period. A new explanation is suggested for the low maternal and high fetal plasma levels of B12.