Bulk flow and diffusion in the cerebrospinal fluid system of the goat

Abstract

Ventriculocisternal perfusions were carried out on chronically prepared, unanesthetized goats. Measurements were made of steady-state rates at which inulin, fructose, creatinine, urea, K, Na, and labeled water (TOH) were removed from perfusion fluid at various hydrostatic and osmotic pressures. The ventricular system is virtually impermeable to inulin. Inulin is removed from subarachnoid spaces by bulk absorption at rates which vary linearly with hydrostatic pressure. Net absorption ceases at –15 cm H₂O. Rate of net formation of cerebrospinal fluid (CSF) is equal to inulin clearance plus the difference between outflow and inflow rates; normally it averages 0.16 cm³ min^–1 and is essentially independent of hydrostatic pressures in the range –10 to +30 cm H₂O. Net rate of formation is linearly related to total osmotic pressure differences between plasma and CSF. The coefficient of osmotic flow is greater than that measured from diffusion of TOH, as in other porous membranes. Passive permeability characteristics resemble those of the vasopressin-treated toad bladder.