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PubMed1955

The placenta and protein metabolism; transfer studies using carbon 14-labeled proteins in dogs.

Plasma proteins tagged in vivo by feeding D-L-lysine-epsilon-C(14) to donor dogs have been administered to pregnant dogs by both oral and intravenous routes. A relatively small percentage of the C(14) activity originally incorporated in these proteins is found to pass from mother to fetus after intravenous injection. The amount transferred tends to increase with the length of gestation period and total number of fetuses. Plasma protein labeled with I(131) does not cross the placenta in the dog, but does in the rabbit. Evans blue dye does not cross the placenta of the dog. After oral administration of labeled plasma protein or lysine, C(14) is transferred promptly and in considerable quantity to the fetus. Labeled plasma proteins disappear more rapidly from the circulation of pregnant than of normal dogs. This increased metabolic turnover occurs without excretion of any excess waste metabolites. The chorionic epithelium, gram for gram, is probably 2 to 3 times as active as the hepatic epithelium in protein metabolism. These findings indicate an important placental function related to maternal and fetal protein metabolism. While the placenta utilizes maternal plasma proteins and amino acids, in a quantitative sense the latter appear to supply the major nitrogen needs of the growing fetus.

Amino Acids↗
PubMed1960

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.

Adult↗