Alpha-fetoprotein and albumin uptake by mouse tissues during development.

We have studied the evolution of the incorporation of alpha-fetoprotein (AFP) and albumin by mouse tissues from fetal to adult life. Mice were injected with 125I-labelled AFP or albumin and, 3 h later, blood and organs were removed and analyzed for their radioactive protein content. Results showed that all immature tissues examined took up both AFP and albumin from blood. AFP uptake was higher during fetal and early postnatal life and decreased with age. In general, the relative uptake of albumin was lower than that of AFP, and the time-course incorporation of both proteins was parallel in brain, liver and kidney. In other tissues such as white adipose tissue, brown adipose tissue and skin. AFP uptake decreased while albumin uptake remained almost constant or increased with age. In the fetal period, the strong AFP uptake in white adipose tissue contrasted with the much lower albumin incorporation by this tissue. Autoradiographs from sections of organs and entire animals confirmed the cytoplasmic localization of AFP and albumin. We conclude that AFP and albumin found in developing tissues, except for fetal liver and yolk sac, proceed mostly from blood uptake. These results agree with recent experimental data suggesting that the major physiological role of AFP is the transport and delivery of polyunsaturated fatty acids to developing tissues.