The metabolism of the retina of the normal and alloxan diabetic rat The levels of oxidised and reduced pyridine nucleotides and the oxidation of the carbon-1 and carbon-6 of glucose

Abstract

The levels of oxidised and reduced NAD and NADP have been determined in the retinae of normal and alloxan-diabetic rats. In the alloxan-diabetic animal the ratios of NAD/NADH2 and of NADPH2/NADP are both reduced, as a result of an increase of NADH2 and a decrease of NADPH2. The relative rates of oxidation of the carbon-1 and carbon-6 of glucose have been studied using C-14 labelled glucose. A C-1/C-6 ratio of 1.13 was obtained for both normal and alloxan-diabetic animals. The levels of the oxidised and reduced co-enzymes in the retina of the normal rat are similar to those of brain and contrast with those of liver; this would suggest a minimum activity for the pentose phosphate pathway. This idea is supported by the ratio of oxidation of C-1/C-6. The co-enzyme changes in the retina of the alloxan-diabetic rat could be taken to infer an increased glycolytic rate, but a reduced rate of breakdown by the shunt mechanism. This possibility is not reflected in the C-1/C-6 ratios. The factors that complicate these interpretations are discussed.