Proteins in cerebrospinal fluid and plasma of fetal pigs during development

The concentrations of total protein, alpha-fetoprotein, fetuin, transferrin and albumin have been measured in cerebrospinal fluid (CSF) and plasma of fetal pigs from 26 to 109 days gestation. Plasma total protein concentration was lowest in the youngest fetuses but thereafter it was between 1,500 and 2,200 mg/100 ml. alpha-Fetoprotein was the predominant plasma protein early in development but its concentration declined throughout the fetal period. alpha-Fetoprotein, fetuin and transferrin accounted for over 65% of the total protein concentration at all fetal ages. Albumin was not detectable in either plasma or CSF at 26 days and did not account for more than 10% of total plasma protein concentration at later stages of gestation; in contrast fetuin was the major protein in plasma (and CSF) later in fetal development. In CSF the concentration of fetuin was highest (178 +/- 8 mg/100 ml) at 26 days. The concentrations of total protein (961 +/- 95 mg/100 ml), alpha-fetoprotein (406 +/- 77 mg/100 ml) and transferrin (195 +/- 19 mg/100 ml) were highest at 31 days after which the concentration of all the main proteins fell very considerably. Albumin was first detected in CSF at 38 days and contributed less than 10% of total protein concentration at later fetal ages. Possible origins of plasma proteins in fetal CSF are discussed. Differences in CSF: plasma ratios for different proteins are consistent with a specific transfer mechanism between their two compartments; but synthesis by fetal choroid plexus or brain has not been excluded.