Blood—cerebrospinal fluid transfer of plasma proteins during fetal development in the sheep

Abstract

The penetration of human and sheep plasma proteins from blood into CSF of sheep fetuses (57-86 days gestation) was studied. The proteins were injected i.v. via cotyledonary vessels. After different time periods the CSF concentrations of marker proteins were estimated by radioactive counting of iodinated human or sheep proteins or by immunoassay of human proteins. Several proteins of similar molecular size penetrated into CSF to a different extent in 60 day fetuses. The steady-state CSF:plasma ratios were about 15% for human AFP [.alpha.-fetoprotein], 10% for human transferrin and sheep albumin, 7% for human .alpha.1-antitrypsin and 5% for human albumin. In older fetuses the penetration of protein from blood into CSF was much reduced and no evidence for differential penetration of different proteins was found. The penetration of human AFP, transferrin and sheep albumin from blood into CSF was greater than can be accounted for by passive diffusion. These results are discussed in relation to those on the identification and quantification of proteins in fetal CSF and plasma. The choroid plexus of the immature (60 days and less) sheep fetus contains a mechanism for the transcellular transfer of plasma proteins which may be selective in nature and of importance for some aspects of brain development.