The movement of sulfate and thiosulfate into in vivo choroid plexus

Abstract The accumulation of sulfate (SO 4 ) and thiosulfate (S 2 O 3 ) in the choroid plexus, brain, and cerebrospinal fluid (CSF) of the rat was measured at various plasma levels of these anions. Increasing the plasma SO 4  or S 2 O 3  concentration levels 40‐ and 580‐fold, respectively, resulted in a linear increase in CSF, brain and choroid plexus concentration of these ions. The relationship between the concentration of these ions in CSF and choroid plexus was also approximately linear over a wide CSF concentration range. In addition, S 2 O 3  did not appear to influence the relation between the concentration of SO 4  in choroid plexus and CSF. The results seem to indicate that there is no saturation of the mechanism responsible for maintaining the low SO 4  or S 2 O 3  concentration in CSF nor does there appear to be competition between these anions for clearance from the CSF. These findings are in conflict with data supporting the active transport of SO 4  and S 2 O 3  from the CSF across the CSF‐blood barrier (choroid plexus).