Glucose Metabolism and α-Keto-acids in Rat Brain and Liver in vivo

Abstract

GLUCOSE is the major substrate for the brain^1,2, which utilizes a very high proportion of the bodily glucose requirement³. Whittam⁴ has calculated that about 40 per cent of the energy produced from glucose metabolism in the brain is required for ion transport mechanisms important in maintaining the physiological function of the tissue. Over the past few years a number of workers^5–8 have demonstrated the high rate of incorporation of carbon-14 from glucose into brain amino-acids, particularly glutamic acid. It has been suggested⁶ that the amino-acids have a special role as intermediates in the brain; that their formation and oxidation constitute a major pathway of glucose metabolism in the brain. However, the characteristically high concentration of free glutamate in the brain, in contrast to other tissues, renders methods of investigations which are based on the labelling of the amino-acid pools, rather than specific activity measurements on individual amino-acids isolated from the tissues, rather inconclusive. As has been suggested⁹, such results could be due to quantitative differences in glycolysis and transamination reactions between the brain and the liver.