Decreased Rate of Glucose Utilization by Rat Brain in Vivo After Exposure to Atmospheres Containing High Concentrations of Co2

Abstract —(1) The effects of exposure of rats to increased atmospheric concentrations of CO 2 on brain metabolism in vivo were studied. (2) After 2·5 min exposure to an atmosphere of 20% CO 2 , the rate of glucose utilization by brain decreased from 0·61 μmol/min per g to 0·32 μmol/min per g and remained between 0·3 and 0·4 μmol/min per g for 60 min, the longest interval studied. O 2 utilization, calculated from the arteriovenous difference of O 2 across the brain and blood flow, was 3·5 μmol/min per g in controls and was 4·7 μmol/min per g after 5 min in the 20% CO 2 atmosphere. (3) The concentrations of glucose, glucose 6‐phosphate and aspartate were increased during the first 10 min of CO 2 exposure whereas the concentrations of other glycolytic intermediates, tricarboxylic acid cycle intermediates and glutamate were decreased. The amount of endogenous substrate which disappeared during the first 10 min was sufficient, if used to supplement glucose as a fuel, to maintain the O 2 consumption at, or slightly above, the control level. Glutamate and lactate were quantitatively the most important energy sources. (4) The mechanism whereby‘CO 2 decreased the rate of glucose utilization is uncertain. The initial rise in glucose 6‐phosphate and fall in fructose 1,6‐diphosphate concentrations suggested that an inhibition of phosphofructokinase was responsible. However, after 60 min in 20% CO 2 , the concentrations of both of these metabolites returned to normal while the rate of glucose utilization remained depressed.