Oxidation of Specifically Labeled Glucose by Rat Adipose Tissue.

Abstract

The in vitro oxidation of glucose-1-C14 and glucose-6-C14 by liver and adipose tissues of the rat was studied. In adipose tissues from normal animals, the yield of C14O2 from glucose-6-C14 averaged about 18% of that obtained from glucose-l-Cl4, indicating the extensive occurrence of extraglycolytic catabolism of glucose. Liver slices from these animals showed a corres-ponding C14O2 ratio of 68%. Starvation (from 18 to 192 hours) depressed the C14O2 yield from glucose- 1-C14 without affecting the yield from glucose-6-C14 in adipose tissues. Similar changes were seen in adipose tissues from alloxan diabetic and cortisone-treated animals. In all these cases, the C-6/C-1 ratio was significantly elevated above normal. In the liver, prolonged starvation (96 to 192 hours) lowered the C14O2 yields from both substrates without affecting their ratio. Marked depressions of C14O2 yields were seen in diabetic livers, but no changes in C-6/C-1 ratio were evident in these, as well as in livers from cortisone-treated rats. Fasted diabetic rats responded to a massive insulin dose with typical symptoms of insulin coma. Adipose tissue oxidation rates of both substrates and their ratio remained characteristically diabetic while the liver ratio approached unity. Previous work indicates that hepatic lipogenesis is abolished under such conditions. Gradual administration of insulin to ad lib fed diabetes resulted in a stimulation of C14O2 yield from glucose-1-C14 without affecting the yield from glucose-6-C14 in adipose tissue. Both C14O2 yields returned to normal levels in the liver with no change in ratio.