Effects of Intraventricular Osmotis Pressure on the Formation Rate of Cerebraspinal Fluid and Subsequent Distribution of Electrolytes Between the Fluid and Serum in Rabbits.

Ventriculocicternal perfusions with artificial CSF were carried out in rabbits. The rate of formation of CSF in the contral animals was found to be 10.9±0.5μl/min. Hypertonic perfusion was performed by adding NaCl or monosaccharides into the perfusion fluid and the osmotic influence these had upon CSF formation was investigated. A remarkable incease in the rate of formation of CSF was observed in the NaCl group, after a steady atate was achieved in the perfusion system, while in the xylose-glucose group, the increase in the rate of formation of CSF was not only less marked but also of shorter duration, despite increased osmolality of the porfusate. In the xylose-glucose group, when the osmotic gradient between porfusate and serum was produced by the addition of sugars to the porfusate, we found that there probably existed a critical ,agnitude of osmotic gradient required in order to initiate osmotic flow through the ependymal linings and/or choroidal epithelium. We estimated this cirtical value to be approximately 30 mOsm/L. Analysis of electrolytes in the effluent revealed no remarkable alteration during perfusion with hyperosmotic slutions when compared with those of the contrals, expect for concentrations of Na+ and Cl- in the NaCl group. The active transport of electrolytes followed by diffusion of water, saturation of a sugar-transport mechanism, and regulation of electrolyte concentration in the ventricular system are all thought to be factors contributing to the homeostatic mechanism which regu