The Effects of Acute Carbon Monoxide Intoxication on the Cerebral Energy Metabolism of the Rat

Abstract

The cerebral metabolic effects of 30 min exposure to 0.5, 1.0, 1.5, and 2.0% carbon monoxide (CO) and 60 min exposure to 1.0% CO were studied in lightly anesthetized rats by measurement of brain tissue contents of glycolytic and citric acid cycle intermediates, as well as tissue energy phosphates. The results indicate that cerebral energy homeostasis is maintained until advanced levels of CO intoxication (2.0%) are reached. Animals exposed to 2.0% CO developed significant decreases in systemic blood pressure, with attendent decreases in cerebral ATP, increases in ADP and AMP, plus early depletions of tissue citrate and α-oxyglutarate. The similarity of this pattern to that previously documented for various cerebral oligemic states suggests a possible modifying role for altered cerebral perfusion in its production. A correlation between conscious behavior and cerebral energy state was suggested by the observation that unanesthetized animals exposed to 1.0% CO for 30 and 60 min retained consciousness, whereas animals exposed to 2.0% CO for 30 min became unresponsive late on in the exposure. A comparison of CO induced changes in intermediary metabolites, energy phosphates, intracellular pH, and cytoplasmic redox state with those seen in hypoxemia indicate no basic qualitative or quantitative differences in the metabolic response of brain tissue to the two conditions.