Newborn and 1-mo-old swine were exposed to identical durations (18 min) and degrees of hypoxia (O-2 content = 4 mL/dL), to examine the effects of hypoxia on cerebral energy metabolism and intracellular pH (pH(i)) in vivo, using P-31 and H-1 nuclear magnetic resonance spectroscopy. Hypoxia produced the same extent of reductions in phosphocreatine (PCr) (63 +/- 28% and 65 +/- 10%, newborns and 1-mo-olds, respectively) and pH(i) (6.93 +/- 0.06 and 6.89 +/- 0.06, respectively) for either age group. The magnitude of changes in PCr, lactate, and pH(i) was larger for subgroups of data collected when cardiovascular instability was present, suggesting that hypotension and possibly reduced cerebral perfusion contributed to cerebral energy failure and lactic-acidosis for either age group. There were no correlations between the blood plasma glucose concentration at 18 min of hypoxia and the extent of change in PCr, lactate, or pH(i) for either age group. During a subsequent period of complete ischemia induced via cardiac arrest after 20 min hypoxia, the decline in PCr and nucleoside triphosphate (NTP), and increase in lactate followed similar rates compared with previously studied age-matched animals that were normoxic before ischemia. The rate constants for the change in PCr, NTP, and lactate during ischemia showed no correlation with the blood plasma glucose concentration measured immediately before cardiac arrest. These results suggest that cerebral glycolytic rates and energy utilization during ischemia are unaffected by a preceding interval of hypoxia and that hyperglycemia does not delay cerebral energy failure during hypoxia or combined hypoxic-ischemia.
