THE EFFECTS OF SYSTEMIC GLUCOSE-CONCENTRATION ON BRAIN METABOLISM FOLLOWING REPEATED BRAIN ISCHEMIA

Since systemic glucose concentration is an important determinant of is chemic brain metabolism in neonates, we sought to determine if the sys temic glucose concentration influences brain metabolic alterations fol lowing repeated partial ischemia. A group of hyperglycemic piglets (n = 12) were compared to a group of modestly hypoglycemic piglets (n = 1 2) using in vivo H-2 and P-31 magnetic resonance spectroscopy to simul taneously measure cerebral blood flow and phosphorylated metabolites b efore, during and 30 min after two 10-min episodes of ischemia (i.e. R ecovery 1 and 2). For both groups, P-ATP levels at Recovery 1 and 2 we re lower than Control (91 +/- 11 and 83 +/- 15% of Control, respective ly for both groups combined, P = 0.002 vs Control). Inorganic phosphor us was elevated in hyperglycemic piglets at Recovery 1 and 2 (117 +/- 15 and 118 +/- 10% of Control). In contrast, in modestly hypoglycemic piglets inorganic phosphorus progressively rose from Recovery 1 (131 /- 24% of Control) to Recovery 2 (149 +/- 137% of Control), and differ ed from the hyperglycemic group (P = 0.02). These changes did not corr elate with post-ischemic cerebral blood flow, cerebral O-2 delivery or cerebral glucose delivery. In both groups phosphocreatine and intrace llular pH returned to Control values during Recovery 1 and 2. The prog ressive increase in inorganic phosphorus post-ischemia in hypoglycemic piglets suggests that modest hypoglycemia during and following repeat ed partial ischemia adversely affects immediate brain metabolic recove ry.