The Formation of Cerebrospinal Fluid in Ventricular Perfusion with Hyperosmolar Fluid

The effects of ventricular fluid hyperosmolality on the CSF formation rate were studied in anesthetized rabbits during ventriculocisternal perfusion. Perfusions were carried out with mock CSF or hypertonic perfusate which was prepared by adding various amounts of either NaCl or glucose to mock CSF. CSF formation rates during perfusions were linearly correlated to differences in osmolality between perfusate and blood plasma (osmotic gradient). The slopes of regression lines in both groups using NaCl (0.032μl/min/mOsm) and glucose (0.035) were similar. Concentration of Na^+ in nascent CSF was reversely correlated to the osmotic gradient in both groups. The slope of regression line was larger in NaCl group (0.585μl/min/mOsm) than in glucose group (0.164). Difference between these two coefficients was statistically significant. ^<22>NaCl and TOH were used as a tracer to estimate the movement of sodium and water from blood to CSF and from CSF to brain during normotonic and hypertonic perfusions. From the results obtained, it is concluded that the net flux of Na_+ into CSF may be regulated in response to osmolality and concentration of Na^+ in the intraventricular CSF. When osmolality of CSF increases, Na^+ is supposed to play a role as a protector against cerebral dehydration due to osmotic flow of water.