Magnesium sulfate attenuates increased blood-brain barrier permeability during insulin-induced hypoglycemia in rats

Magnesium probably protects brain tissue against the effects of cerebral is chemia, brain injury and stroke through its actions as a calcium antagonist and inhibitor of excitatory amino acids. The effects of magnesium sulfate on cerebrovascular permeability to a dye, Evans blue, were studied during i nsulin-induced hypoglycemia with hypothermia in rats. Hypoglycemia was indu ced by an intramuscular injection of insulin. After giving insulin, each an imal received MgSO4 (270 mg/kg) ip, followed by a 27 mg/kg dose every 20 mi n for 2.5 h. Plasma glucose and Mg2+ levels of animals were measured. Magne sium concentrations increased in the serum following MgSO4 administration ( 6.05 +/- 0.57 vs. 2.58 +/- 0.14 mg/dL in the Mg2+ group, and 7.14 +/- 0.42 vs. 2.78 +/- 0.06 mg/dL in the insulin + Mg2+ group, P < 0.01). Plasma gluc ose levels decreased following hypoglycemia (4 +/- 0.66 vs. 118 +/- 2.23 mg /dL in the insulin group, and 7 +/- 1.59 vs. 118 +/- 4.84 mg/dL in the insu lin + Mg2+ group, P < 0.01). Blood-brain barrier permeability to Evans blue considerably increased in hypoglycemic rats (P < 0.01). In contrast, blood -brain barrier permeability to Evans blue was significantly reduced in trea tment of hypoglycemic rats with MgSO4 (P < 0.01). These results indicate th at Mg2+ greatly reduced the passage of exogenous vascular tracer bound to a lbumin into the brain during hypoglycemia with hypothermia. Mg2+ could have protective effects on blood-brain barrier permeability against insulin-ind uced hypoglycemia.