THE LOCI of cerebrospinal fluid (CSF) resorption pathways are controversial, and the site of amino acid resorption has never been studied. We have investigated the reabsorption from rat CSF of methionine S35, using a readily reproducible technique to avoid uncertainties of previous methods.
Key and Retzius,1 and Weed2,3 laid the basis for the concept that the CSF is absorbed mainly through the arachnoidal villi. Many recent experiments lend support to their view. Hoffmann and Thiel4 (in monkey) and Welch5 (in man) have demonstrated histologically that the arach-noid villi can work valves to excrete the CSF. Many drugs,6-8 dextran and inulin,9 magnesium and calcium,10-13 and sucrose14 probably leave the CSF by mechanical drainage through the villi.
However, it is likely that some substances have another resorption pathway from the CSF. The choroid plexus of the fourth ventricle concentrates iodopyracet (Diodrast) and phenolsulfonphthalein