Dynamics of distribution of 3H-inulin between the cerebrospinal fluid compartments

Since the distribution of substances between various cerebrospinal fluid (CSF) compartments is poorly understood, we studied 3H-inulin distribution, over time, after its injection into cisterna magna (CM) or lateral ventricle (LV) or cisterna corporis callosi (CCC) in dogs. After the injection into CM 3H-inulin was well distributed to cisterna basalis (CB), lumbar (LSS) and cortical (CSS) subarachnoid spaces and less distributed to LV. When injected in LV 3H-inulin was well distributed to all CSF compartments. However, after injection into CCC 3H-inulin was mostly localized in CCC and adjacent CSS, while its concentrations were much lower in CM and CB and very low in LSS and LV. Concentrations of 3H-inulin in venous plasma of superior sagittal sinus and arterial plasma were very low and did not differ significantly, while its concentration in urine was very high. In 3H-inulin distribution it seems that two simultaneous processes are relevant: a) the pulsation of CSF with to-and-fro displacement of CSF and its mixing, carrying 3H-inulin in all directions, and b) the passage of 3H-inulin from CSF into nervous parenchyma and its rapid distribution to a huge surface area of capillaries by vessels pulsations. 3H-inulin then slowly diffuses across capillary walls into the bloodstream to be eliminated in the urine.