Cerebral oxidative metabolism and redox state during hypoxia-ischemia and early recovery in immature rats.
Intracellular pH (pHi) and cytoplasmic and mitochondrial oxidation-reduction (redox) states of cerebral tissue were examined in relation to perturbations of glycolytic and tricarboxylic acid cycle intermediates and of high-energy phosphate reserves during hypoxia-ischemia and the early recovery period in the immature rat. Seven-day postnatal rats underwent unilateral common carotid artery ligation and exposure to 8% O2 for 3 h, after which they were quick frozen in liquid N2 at the terminus of hypoxia-ischemia and at 10, 30, 60, and 240 min of recovery for enzymatic fluorometric analysis of cerebral metabolites. During hypoxia-ischemia, concentrations of glucose and alpha-ketoglutarate in the cerebral hemisphere ipsilateral to the carotid artery occlusion were depleted to 10 and 70% of control, respectively; pyruvate was unchanged. During recovery, glucose, pyruvate, and alpha-ketoglutarate increased above their respective control values. Calculated pHi decreased from 7.0 (control) to 6.6 during hypoxia-ischemia and normalized by 10 min of recovery. The cytoplasmic NAD+/NADH ratio decreased (increased reduction) to 50% of control during hypoxia-ischemia and remained in the reduced state throughout 4 h of recovery. Paradoxically, mitochondrial NAD+/NADH was oxidized at the terminus of hypoxia-ischemia. The mitochondrial oxidation which developed during hypoxia-ischemia presumably results from a limitation of cellular substrate (glucose) supply, which in turn leads to a depletion of high-energy phosphate reserves, culminating in brain damage.
Yager
J Y
JY
Department of Pediatrics (Pediatric Neurology), Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Brucklacher
R M
RM
Vannucci
R C
RC
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000378:metabolism*; D002545:Brain Ischemia / Q000378:metabolism*; D002952:Citric Acid Cycle; D003593:Cytoplasm / Q000378:metabolism; D006019:Glycolysis; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats