Transfer of Magnesium across the Perfused Choroid Plexus of Sheep

Abstract

Isolated perfused choroid plexus preparations from sheep were used to study the effects of low concentrations of magnesium in the perfusion fluid on the transfer of magnesium into choroid plexus fluid (CPF). A perfusion fluid of similar electrolyte composition to sheep blood resulted in CPF similar to ventricular cerebrospinal fluid at a rate of 2·2 III min -1 mg -I dry choroidal tissue. Decreasing the concentration of magnesium in the perfusion fluid caused a fall in the concentration of magnesium in the CPF, although it remained higher than in the perfusion fluid. The rate of transfer of magnesium from the perfusion fluid to the CPF decreased in the presence of high levels of potassium in the perfusion fluid. But decreasing the concentration of calcium in the perfusion fluid had no effect on magnesium transfer rates.These results suggest that the ability of the choroid plexus to transport magnesium against a concentration gradient is an important control of the concentration of the cerebrospinal fluid. However, this ability is insufficient to maintain cerebrospinal fluid concentrations of magnesium at normal levels when the blood magnesium concentration is below about 0'5 mmoll-I .Extra keyword: hypomagnesaemia.

Basic considerations on magnesium in the management of neurocritical patients

“…Animal studies have shown that Mg can cross the blood-brain barrier and is transported across the barrier with a net flow from the blood to the parenchyma [37][38][39]. The active transport of Mg from the blood to the extracellular fluid of the brain is evidenced by its higher concentration in the extracellular cortical fluid than in the plasma dialysate or cisternal cerebrospinal fluid [38,39].…”

“…Animal studies have shown that Mg can cross the blood-brain barrier and is transported across the barrier with a net flow from the blood to the parenchyma [37][38][39]. The active transport of Mg from the blood to the extracellular fluid of the brain is evidenced by its higher concentration in the extracellular cortical fluid than in the plasma dialysate or cisternal cerebrospinal fluid [38,39]. Another interesting finding is that Mg administration could atten-uate cell death secondary to alterations in the cytoskeleton and, therefore, reduce apoptosis due to p53 expression after brain trauma [1].…”