Magnesium exchange between blood and cerebrospinal fluid.

OPPELT, W. W., I. MACINTYRE, AND D. P. RALL. Magnesium exchange between blood and cerebrospinal @id. Am. J. Physiol. 205(s) : 959-962. 1 g63.-Magnesium exchange between plasma and cerebrospinal fluid (CSF) was studied in dogs using Mg2*C12 and MgClz. Normal CSF/plasma magnesium ratio in this animal is I .34. In face of a plasma magnesium concentration 300-400~~ of normal, the CSF magnesium only rose to a maximum of 2 I yi above control at the <end of 5.5 hr. Intravenously injected Mg2*C1z 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.