CYCLOHEXITOL TRANSPORT IN THE CENTRAL NERVOUS SYSTEM

Abstract

SUMMARY: Mammalian brain and cerebrospinal fluid (CSF) normally contain about 100 and 5 times respectively as much unbound myo-inositol as does plasma (0.1 mM). In brain, about 50 percent of the accounted for unbound myo-inositol is synthesized from glucose and 50 percent enters brain from blood by a saturable transport system. In CSF, about 33 persent of the accounted for unbound myo-inositol is synthesized from glucose in brain whereas 67 percent enters CSF from blood by a saturable transport system. The choroid plexus, the anatomical location of the blood-CSF barrier, is a locus for myo-inositol transport from blood into CSF. The myo-inositol transport system within the choroid plexus is saturable, concentrative and energy-dependent. Of the 8 cyclohexitol stereoisomers tested, only myo-inositol and scyllitol had high affinity (0.1 mM) for the cyclohexitol transport system in choroid plexus. In vivo, the choroid plexus helps maintain the CSF (and indirectly brain) myo-inositol concentration at fairly constant levels by regulating myo-inositol transport from plasma into CSF.