[Effects of hypo- or hyperglycemia on brain metabolism in experimental cerebral ischemia]

Glucose, lactate, pyruvate and adenosine triphosphate (ATP) concentrations in the supratentorial brain tissue frozen in situ were measured one hour after bilateral carotid occlusion in spontaneously hypertensive rats, of which blood glucose levels were varied by intraperitoneally injected insulin (hypoglycemia), saline (normoglycemia) and 50% glucose (hyperglycemia). Cerebral glucose concentrations as well as blood glucose levels were significantly increased in hyperglycemic animals, and decreased in hypoglycemic ones. Cerebral lactate, and lactate/pyruvate ratio at one-hour ischemia tended to increase in hyperglycemic animals comparing with those in normoglycemic ones, although cerebral ATP levels were slightly higher in the former. In hypoglycemic animals with one-hour ischemia, cerebral lactate was less increased but ATP was significantly reduced. It has been reported that hyperglycemia has vulnerable effects on brain metabolism of complete cerebral ischemia, presumably due to hyperglycemia-induced lactic acidosis of the brain. In incomplete cerebral ischemia as demonstrated in the present study, however, ATP concentrations remained at slightly higher level, despite tendency to more increase in lactate in hyperglycemic animals, indicating that high blood glucose level might be beneficial, rather than vulnerable, to incomplete cerebral ischemia. On the other hand, hypoglycemia causes more severe impairment of the brain energy metabolism because of an insufficient supply of substrates to the brain.