Factors affecting distribution of iodide in brain and cerebrospinal fluid

The effects of acetazolamide, sodium perchlorate, ouabain, and of iodide loading on the processes controlling I131 and inulin-C14 distribution in the brain and CSF were studied in nephrectomized rats. It was observed that the first three drugs increased the concentration of both iodide and inulin in the brain and CSF after intracisternal administration of the tracers. It was concluded that acetazolamide reduced the rate of formation and flow of CSF, that perchlorate primarily decreased active iodide transport, and that ouabain slightly reduced CSF formation and flow. Iodide loading increased the CSF/plasma iodide ratio, expressed as percent (CSF iodide space), from 1.97 to 42.17, and the comparable values for brain were 2.02 and 11.76, respectively. The results suggest that the primary factors in the control of iodide distribution in the CNS are the following: 1) an active iodide transport system between CSF and blood, 2) limited permeability to iodide of the structures between blood and CSF and between blood and brain, and 3) relatively free diffusion of iodide between brain and CSF.