Rat Alpha₁ Fetoprotein. V. Catabolism and Fetal-Maternal Distribution

Summary

The rates of catabolism and the distribution of alpha₁ fetoprotein (α₁F) in the rat during gestation were determined with the use of radiolabeled, highly purified α₁F, and the serum α₁F concentrations were measured by radioimmunoassay. The concentration of α₁F at term was 5000 µg/ml in fetal serum, 1500 µg/ml in amniotic fluid, and 200 µg/ml in maternal serum. There was an equilibration of α₁F between fetal blood, amniotic fluid, and maternal blood. The half-life of α₁F in normal and lactating rats was 1 day. But, in pregnant rats, it was 12–15 hours. This was due to a catabolic site in the fetus or placenta that could be identified during the last week of gestation. This was not specific for α₁F, since the catabolism of albumin was also more rapid in pregnant than in normal or lactating rats. The physiologic function of α₁F remains unknown.