Cerebral energy metabolism and intracellular pH during severe hypoxia and recovery: A study using 1H, 31P, and 1H [13C] nuclear magnetic resonance spectroscopy in the guinea pig cerebral cortex in vitro

Abstract

1H and 31P nuclear magnetic resonance spectroscopy was used to study intracellular pH (pHi), high-energy phosphates, lactate, and amino acids in cortical brain slices superfused in Krebs-Henseleit bicarbonate buffer during and after severe hypoxia at 0, 10, and 50 mM glucose. An extensive drop in phosphocreatine (PCr) and a rapid build-up of intracellular lactate and H+ were the first signs of hypoxia. Adenosine triphosphate (ATP) was significantly more resistant to hypoxia provided that glucose was present. In the preparations that had been exposed to hypoxia in the presence of glucose, PCr became detectable within 2 min of reoxygenation, and both PCr and ATP concentrations were restored to 72-80% of normoxic levels within 30 min. Lactate was washed out, and pHi returned to normal within 4-8 min. Using 1-[13C]glucose as a tracer, we demonstrated that the rate of lactate production in the immediate posthypoxic period was at the prehypoxic level, indicating that the elevated lactate during this period was due solely to that produced during hypoxia. During reoxygenation of the preparations that were denied glucose during hypoxia, only 30% of total creatine + PCr and 18% of PCr were restored, and ATP was not detectable. The lactate concentration rose twofold in this period, and pHi became significantly more alkaline than before the hypoxic insult. Thus acute metabolic damage was considerably greater if glucose was absent during the insult, suggesting that either anaerobic ATP production or low pH may exert some protective effect against acute cell damage.