Carbohydrate and Energy Metabolism during the Evolution of Hypoxic-Ischemic Brain Damage in the Immature Rat

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Abstract
The brain damage that evolves from perinatal cerebral hypoxia-ischemia may involve lingering disturbances in metabolic activity that proceed into the recovery period. To clarify this issue, we determined the carbohydrate and energy status of cerebral tissue using enzymatic, fluorometric techniques in an experimental model of perinatal hypoxic-ischemic brain damage. Seven-day postnatal rats were subjected to unilateral common carotid artery ligation followed by 3 h of hypoxia with 8% oxygen at 37°C. This insult is known to produce tissue injury (selective neuronal necrosis or infarction) predominantly in the cerebral hemisphere ipsilateral to the carotid artery occlusion in 92% of the animals. Rat pups were quick-frozen in liquid nitrogen at 0, 1, 4, 12, 24, or 72 h of recovery; littermate controls underwent neither ligation nor hypoxia. Glucose in both cerebral hemispheres was nearly completely exhausted during hypoxia-ischemia, with concurrent increases in lactate to 10 mmol/kg. During recovery, glucose promptly increased above control values, suggesting an inhibition of glycolytic flux, as documented in the ipsilateral cerebral hemisphere by measurement of glucose utilization (CMRglc) at 24 h. Tissue lactate declined rapidly during recovery but remained slightly elevated in the ipsilateral hemisphere for 12 h. Phosphocreatine (P∼Cr) and ATP in the ipsilateral cerebral hemisphere were 14 and 26% of control (p < 0.001) at the end of hypoxia-ischemia; total adenine nucleotides (ATP + ADP + AMP) also were partially depleted (–46%). During the first hour of recovery, mean P∼Cr was replenished to within 90% of baseline, whereas mean ATP was incompletely restored to 68–81% of control (p < 0.05). Individual ATP and total adenine nucleotide values were >2 SD below control levels in 17/24 (71%) brains at all intervals of recovery. Both ATP and total adenine nucleotides were inversely correlated with tissue water content, reflecting the extent of cerebral edema. No major alterations in the high-energy phosphate reserves occurred in the contralateral cerebral hemisphere either during or following hypoxia-ischemia. Thus, following perinatal cerebral hypoxia-ischemia, ATP and total adenine nucleotides never recover completely in brains undergoing damage but rather are permanently depleted to levels that reflect the severity of tissue injury. Recovery of P∼Cr to near normal levels can occur despite evolving brain damage. The findings have relevance to the assessment of asphyxiated newborn humans using magnetic resonance spectroscopy.