The influence of the choroid plexus on the concentration of prealbumin in CSF.

Prealbumin and albumin concentrations were measured in homogenates of choroid plexus, ventricular and lumbar CSF, and in serum. The passive permeability-independent prealbumin concentration was estimated by subtracting from the total concentration that portion which enters the plexus and CSF by a passive molecular sieve effect, assuming that the diffusion of albumin and prealbumin is similar. The passive permeability-independent prealbumin concentration was highest in homogenates of the choroid plexus (mean = 56 micrograms/g). It was almost 3 times that in ventricular CSF (mean = 18 micrograms/ml). The passive permeability-independent concentration decreased only slightly during passage from the ventricular to the lumbar CSF space (mean = 16 micrograms/ml). These data suggest that much of the prealbumin in CSF enters the ventricular CSF via the choroid plexus by a mechanism different from that responsible for the transit of albumin.