NMR Spectroscopic Investigation of the Recovery of Energy and Acid—Base Homeostasis in the Cat Brain after Prolonged Ischemia

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Abstract
The effects of 1 h of complete global ischemia on the recovery of high-energy phosphates, intracellular pH (pHi), and lactate in the cat brain in vivo was investigated by 31P and 1H NMR spectroscopy. Ischemia led to a decrease in creatine phosphate (CrP), nucleoside triphosphates (NTP), and pHi, while inorganic phosphate and lactate increased. Intracellular pH decreased from a control value of 7.07 ± 0.04 to 6.17 ± 0.12 after 1 h of ischemia ( N = 7). The degree of metabolic recovery after recirculation was variable. In three animals CrP and NTP were detected within 4 min and NTP increased to ≥90% of control within 1 h; these levels were maintained for the 3 h of observation. In four other animals, CrP and NTP reached only 20 to 80% of control; however, high-energy phosphates decreased and lactate increased spontaneously between 1 and 2.5 h. Immediately following recirculation, pHi decreased further by an average of 0.3 units. The rate of recovery of cerebral pHi was slower than that of PCr and NTP for the majority of animals. Recovery of pHi was not detected for an average of 32 min after recirculation—by this time, NTP had attained 80 ± 10% of their preischemic level. Recovery of pHi (and lactate) was not observed in two animals where PCr and NTP recovered transiently to only 30–43% of the preischemic level. Recovery of cerebral pHi was markedly heterogeneous in one animal, since two Pi peaks were detected shortly after recirculation. No correlation was found between the maximum levels of CrP and NTP attained after recirculation and the value of pHi during ischemia.

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