Magnesium exchange between plasma and cerebrospinal fluid (CSF) was studied in dogs using Mg28Cl2 and MgCl2. Normal CSF/plasma magnesium ratio in this animal is 1.34. In face of a plasma magnesium concentration 300–400% of normal, the CSF magnesium only rose to a maximum of 21% above control at the end of 5.5 hr. Intravenously injected Mg28Cl2 enters the CSF rapidly, reaching equilibrium within 2–3 hr. The exit rate of magnesium from the CSF has a half time of about 70 min when CSF magnesium levels are close to normal or they are greatly elevated. This rate is not affected by increasing plasma magnesium concentrations. It is concluded that an active transport mechanism is involved in transporting magnesium from blood to CSF, and that diffusion and bulk filtration are responsible for the removal from the CSF.
- active transport
- blood-CSF barrier
- bulk flow
- Copyright © 1963 by American Physiological Society