Transferrin in fetal sheep cerebrospinal fluid and plasma during gestation.

1. Transferrin concentrations in fetal sheep CSF and plasma have been estimated between 31 and 125 days gestation and in the adult, using a radial immunodiffusion assay. 2. The plasma concentration was lowest (183 +/- 35 mg/100 ml) in the earliest fetuses examined (31 days). It increased to over 350 mg/100 ml by 35 days; thereafter it was around the adult value (580 mg/100 ml). 3. In CSF the transferrin concentration increased from 43 +/- 10 mg/100 ml at 31 days to a maximum of 163 +/- 14 mg/100 ml at 40 days gestation after which it decreased considerably to 6.1 +/- 0.7 mg/100 ml at 125 days and was even lower in the adult (1.1 +/- 0.2 mg/100 ml). 4. CSF: plasma ratios for transferrin especially when compared with those of other plasma proteins, are not compatible with passive leakage of protein from blood to CSF in the developing brain. The results may be explained by specific transfer of proteins into CSF but synthesis by the choroid plexus or brain has not been excluded.