Resistance of diabetic rat electroretinogram to hypoxemia

Purpose. To investigate the mechanisms of the known electroretinographic 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 electroretinogram. Normoxic and hypoxemic recordings were taken from nine normal and six streptozotocin- diabetic, anesthetized, paralyzed, and ventilated pigmented rats. Results. When inspired O₂ was reduced the retinal pigment epithelial c-wave component of most of the normal rats diminished, whereas those of the diabetic rats, though initially smaller, were more resistant to the episode of hypoxemia (P = 0.0061). A similar trend was seen in other components. Conclusion. It is proposed that the reduced sensitivity of the diabetic electroretinogram to hypoxemia results from a reduced dependency of the diabetic retina on oxygen. This reduced dependence may follow from a shift in adenosine triphosphate production whereby oxidative phosphorylation is reduced by the high level of retinal intracellular glucose (Crabtree effect). A reduced oxygen demand would cause a transient increase in retinal PO₂, leading to a reduction in retinal blood flow. The resulting chronic hypoperfusion of the retinal circulation may deprive the retina of vital, non-energy-related substances.