Impaired permeability of the blood-cerebrospinal fluid barrier in hyperphenylalaninaemia.

In hyperphenylalaninaemic rats the accumulation of 5-hydroxytryptophan (5-HTP) in the cerebrospinal fluid (CSF) could be shown in spite of the fact, that the 5-HTP levels of serum and brain remain constant. In vitro studies of the influx and efflux of 5-HTP and phenylalanine on isolated beef choroid plexus suggested that both aminoacids use the same carrier system. It is concluded that a high concentration of phenylalanine inhibits the re-uptake of 5-HTP by the endothelial cells of the choroid plexus. Additionally, an increased efflux of 5-HTP from choroid plexus leads to the accumulation of 5-HTP in the cerebrospinal fluid.