Metabolite changes in neonatal rat brain during and after cerebral hypoxia-ischemia: a magnetic resonance spectroscopic imaging study

Cerebral metabolite concentrations were measured in infant rats using proto n magnetic resonance spectroscopic imaging. Measurements were made prior to , during and after exposure of rats (6- and 7-day-old) to unilateral cerebr al hypoxia-ischemia (right carotid artery occlusion +2 h 8% oxygen). Data c lustered according to age and outcome-6-day-old animals with no infarct and 7-day-old animals with infarct, In 6-day-old animals, cerebral lactate con centration increased during hypoxia-ischemia, particularly ipsilateral to t he occlusion, and returned to normal soon after the end of hypoxia. There w ere no major changes in N-acetyl-aspartate levels (NAA) in this group and n o regions of hyperintensity on T-2 or DW weighted images at 24 h. In the 7- day-old animals, lactate increased during hypoxia-ischemia and remained ele vated in the first hour after reperfusion, Furthermore, lactate remained at 258 +/- 117% and 233 +/- 56% of pre-hypoxic levels, 24 and 48 h post-hypox ia, respectively. NAA concentrations ipsilateral to the occlusion decreased to 55 +/- 14% during hypoxia, recovered early post-hypoxia and again decre ased to 61 +/- 25% and 41 +/- 28% at 24 and 48 h post hypoxia-ischemia, res pectively. The infarct volumes measured by diffusion weighted and T-2 weigh ted MRI at 48 h post-hypoxia were 152 +/- 40 mm(3) and 172 +/- 35 mm3, resp ectively. Thus, irreversible damage correlated well with measured ill vivo lactate and NAA changes. Those animals in which NAA was unaltered and lacta te recovered soon after hypoxia did not show long-term damage (6-day-old an imals), whereas those animals in which NAA decreased and lactate remained e levated went on to infarction (7-day-old animals). Copyright (C) 1999 John Wiley & Sons, Ltd.