Cerebral energy state during or after hypoxia and complete or incomplete ischemia

Abstract

The behavior of fuels (glycogen and glucose), of glycolytic pathway intermediates (G-6-P and pyruvate), of the end product (lactate), and of the pool of labile phosphates (ATP, ADP, AMP and creatine phosphate), and the energy charge of the brain were studied in the motor area of the cerebral cortex of beagle dogs in hypovolemic hypotension (mean arterial blood pressure, 55 Torr). These parameters were evaluated after acute hypoxia, obtained by altering the composition of the inhalation mixture; after acute hypoxia plus incomplete ischemia; after acute hypoxia plus complete ischemia; during posthypoxic recovery (3, 15, or 30 min after the restoration of normal ventilation); and during posthypoxic recovery and recirculation after hypoxia with complete or incomplete ischemia. A comparative examination of the different conditions showed that the most dramatic fall in the cerebral energy state took place during hypoxia plus complete ischemia followed, in order, by hypoxia plus incomplete ischemia and simple hypoxia. Reversal was most difficult in hypoxia plus incomplete ischemia. The different situations were discussed in relation to changes taking place in cerebral biochemical events. The level of cerebral energy decay (as measured by the energy charge potential) does not appear to be the rate-limiting factor for posthypoxic or postischemic recovery.