EFFECT OF ACTIVE-TRANSPORT ON DISTRIBUTION AND CONCENTRATION GRADIENTS OF [H-3] BENZYLPENICILLIN IN THE CEREBROSPINAL-FLUID

After application of [H-3]benzylpenicillin ([H-3]BP) in lateral brain ventricle in dogs, the distribution of [H-3]BP to contralateral ventri cle and cisterna magna was much higher when its active transport from cerebrospinal fluid (CSF) was blocked by probenecid than under control conditions. Analysis of [H-3]BP concentrations in both lateral ventri cles and cisterna magna over time indicates that active transport rest ricts distribution of substances along CSF spaces and contributes to t he maintenance of their concentration gradients between CSF compartmen ts. This suggests that biochemical changes in a part of the brain and the adjacent CSF compartment may not be reflected into remote compartm ents of CSF such as lumbar CSF if substances in question are removed f rom CSF by active transport.