Chronic hypoxemia causes extracellular glutamate concentration to increase in the cerebral cortex of the near-term fetal sheep.

Fetal hypoxia is an important cause of neurologic morbidity and mortality. Hypoxia-induced increase in extracellular glutamate concentration can lead to excitotoxic neuronal death in adults. The objective of this study was to test whether chronic fetal hypoxemia increases extracellular glutamate concentration in the unanesthetized intact cerebral cortex of the near-term fetal sheep. Microdialysis probes were implanted into the parasagittal parietal cortex and periventricular white matter of near-term fetal sheep. At 124 +/- 1 days of gestation, extracellular glutamate concentration was determined before and during 24 h of fetal hypoxemia. Chronic hypoxemia was produced by tightening a vascular occluder placed around the maternal common iliac artery. Larger decreases in fetal arterial oxygen content were associated with larger increases in extracellular glutamate concentration in the parietal cortex (Kendall's tau = 0.81, N = 7, p = 0.005). No such relationship was detected in the periventricular white matter. Chronic hypoxemia increases extracellular glutamate concentration in the intact cerebral cortex of the unanesthetized near-term fetal sheep.