RESISTANCE OF DIABETIC RAT ELECTRORETINOGRAM TO HYPOXEMIA

Purpose. To investigate the mechanisms of the known electroretinograph ic abnormalities of diabetic rats and to explore effects of hypoxemia. Methods. Subretinal and vitreal microelectrodes were used to isolate the retinal and retinal pigment epithelial components of the electrore tinogram. Normoxic and hypoxemic recordings were taken from nine norma l and six streptozotocin-diabetic, anesthetized, paralyzed, and ventil ated pigmented rats. Results. When inspired O2 was reduced the retinal pigment epithelial c-wave component of most of the normal rats dimini shed, whereas those of the diabetic rats, though initially smaller, we re more resistant to the episode of hypoxemia (P = 0.0061). A similar trend was seen in other components. Conclusion. It is proposed that th e reduced sensitivity of the diabetic electroretinogram to hypoxemia r esults from a reduced dependency of the diabetic retina on oxygen. Thi s reduced dependence may follow from a shift in adenosine triphosphate production whereby oxidative phosphorylation is reduced by the high l evel of retinal intracellular glucose (Crabtree effect). A reduced oxy gen demand would cause a transient increase in retinal PO2, leading to a reduction in retinal blood flow. The resulting chronic hypoperfusio n of the retinal circulation may deprive the retina of vital, non-ener gy-related substances.