Histochemistry of the Retina in the Alloxan-diabetic Rat.

THERE have been relatively few studies of the carbohydrate metabolism of the retina of the alloxan-diabetic animal and not all have been in agreement. Illing and Gray (1951) described an impairment of glucose utilization in the retina of diabetic rabbits, but these results were not confirmed by Kornblueth, Yardeni-Yaron, and Wertheimer (1953). DeRoetth and Pei (1960), using manometric techniques, found decreased anaerobic glycolysis and increased succinic dehydrogenase activity in the retina of alloxan-diabetic rats compared with normal controls. Heath, Rutter and Beck (1962) demonstrated an increase in the nicotinamide-adenine nucleotide content of the alloxan-diabetic rat and a decrease in the reduced form of this nucleotide. Kurimoto and Newell (1963), using histochemical techniques, have shown an increased phosphorylase activity in the alloxan-diabetic rat retina. Additionally, retinal and renal glycogen which was not mobilized by starvation as was liver glycogen was demonstrated. It was the purpose of this study to investigate histochemically some of the pathways of glucose metabolism in the normal and the alloxan-diabetic rat. The metabolic pathways of the retina may be studied by means of enzymatic, micro-enzymatic, or histochemical techniques. The usual enzymatic techniques involve the incubation of large segments of the retina with appropriate substrates and measurement of the amount of oxygen used or metabolic products formed. The micro-enzymatic method, as developed by Lowry, Roberts, and Lewis (1956) and Lowry, Roberts, Schulz, Clow, and Clark (1961) provides the most accurate quantitative estimate of enzyme activity in the retina, but permits study solely of one individual layer at a time. Histochemical techniques provide a visualization of a cross-section of the distribution of an enzyme system. These latter techniques, however, depend upon interaction of more than one enzyme and during incubation enzymes may diffuse into adjacent retinal layers so that specific localization enzyme may not be accurate.