Pathways of glucose catabolism in rat liver in alloxan diabetes and hyperthyroidism

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Abstract
Rat-liver slices were incubated with (1-C14) glucose and with (6-C14) glucose, and the yields of C14O2 from these two substrates were compared in normal, alloxan-diabetic, insulin-treated diabetic and thyroxine-treated animals. Livers from the same animals were used for determining the activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and of phospho-glucose isomerase. In addition, glucose 6-phosphatase activity was determined in the control and hyperthyroid-rat livers. In diabetes the formation of C14O2 from (6-C14) glucose is significantly reduced, whereas that from (1-C14) glucose is only very slightly reduced. This indicates a decrease in the relative proportion of glucose catabolized via glycolysis. Treatment of diabetic rats with insulin partially reverses the changes mentioned above by increasing the C14O2 production from both (1-C14) - glucose and (6-C14) glucose, with an accompanying fall in the quotient (yield of C14O2 from (1-C14) - glucose) /(yield of C14O2 from (6-C14) glucose. The levels of activity of glucose 6-phosphate and 6-phosphogluconate dehydrogenases are also increased, glucose 6-phosphate dehydrogenase activity being significantly higher than that of normal liver. After thyroxine treatment C14O2 production from (6-C14) glucose is significantly increased, whereas that from (1-C14) glucose is only very slightly increased, indicating greater participtation of the glycolytic pathway. Glucose 6-phosphatase activity is significantly higher in the livers of thyroxine-treated rats.