Synthesis of plasma proteins by rat fetal brain and choroid plexus

Several plasma proteins have previously been demonstrated to be within cells (presumed neurons) in the developing brain of various species. The possibility that the plasma proteins α-fetoprotein (AFP) albumin and transferrin may be synthesized by developing brain and choroid plexus has been investigated in fetal rats of 18 to 22 days gestation. Samples of these tissues and of liver were incubated in Krebs solution containing [(3)H]leucine at 37°C for 1 h. Radioactively labelled AFP, albumin and transferrin were extracted and separated by immunoprecipitation. Incorporation of [(3)H]leucine into the plasma proteins was demonstrated in both fetal brain and choroid plexus. Incorporation was completely blocked by cycloheximide. It is concluded that fetal brain and choroid plexus synthesize AFP, albumin and transferrin and that secretion of these proteins by developing brain and choroid plexus cells probably contributes to the high concentration of plasma proteins in fetal csf.