Acute-phase α2-macroglobulin in csf during development of the fetal rat

The concentration of acute phase α2-macroglobulin (APα2M) was measured in the cerebrospinal fluid (csf) and plasma of fetal (12-22 days gestation) and neonatal (0-10 days post partum) rats. APα2M was detectable in the fetus as early as samples could be obtained (12 days) and increased in both fluids to reach a peak near the time of birth (17 mg/100 ml in csf and 168 mg/100 ml in plasma). During the neonatal period APα2M concentration declined markedly in both fluids. The results are compared with values for albumin and α-fetoprotein in fetal rats. It was concluded that maintenance of the csf:plasma ratios for the three proteins are incompatible with an explanation of passive diffusion from plasma to csf. Other mechanisms to explain the occurrence of high concentrations of plasma proteins in fetal csf are discussed.