Experimental quantitative evaluation of transvascular removal of unnecessary substances in brain edema fluid.

We developed a model by which the transvascular removal of unnecessary substances in brain edema fluid could be measured quantitatively and chronologically. Brain stab wounds were produced in Wistar rats by insertion of paired microdialysis probes in the unilateral caudatoputamen. Homovanillic acid (HVA) was administered by microdialysis from one probe, and the HVA clearance was measured by HPLC analysis of perfusate from the other probe. Using this model, we evaluated the site of removal and whether the removal processes were affected by anesthesia or an elevated plasma concentration of the substance. As a result, 1) Probenecid did not change HVA clearance although this inhibits HVA removal via subarachnoid vessels. Therefore, HVA removal in this model was considered mainly due to intraparenchymal transvascular efflux. 2) There was no alteration in HVA removal induced by anesthesia or intravenous HVA injection. Consequently, this efflux mechanism seems to be a rather stable protective process, and seems to play a considerable role in brain microenvironmental homeostasis.