Retinal glucose metabolism and blood flow : Effects of photic stimulation

Abstract: Retinal glucose metabolism was investigated under different light conditions in cats,pigs and rabbits. Glycolysis and glucose oxidation in the outer and inner parts of theretina were assessed by determining arteriovenous concentration differences foroxygen, glucose and lactate, as well as local blood flow. In all of the species studied, more than half of the glucose used was catabolized tolactate. In the outer part of the retina in cats and pigs, 10-20% was oxidized. In theinner retina, studied only in pigs, 70% of the glucose consumed was oxidized. In boththe inner and outer parts of the retina, most of the lactate formation remained underhyperoxia, indicating aerobic glycolysis. In eyes previously dark-adapted, constant light caused up to 60% reduction inglycolysis and 20-40% reduction in glucose oxidation in the outer retina in cats andpigs. No clear effects were observed in rabbits. Flicker increased glucose metabolismin rabbits, and blood flow in both the retina and optic nerve head in cats. The lattereffect could be abolished by a nitric oxide synthase inhibitor, which also produced astrong vasoconstriction in the optic nerve head in cats. In conclusion, most of the glucose used in the retina is aerobically metabolized tolactate in each of the three species. Constant light inhibits glucose metabolism in theouter retina in cats and pigs, but has little effect in rabbits, while flicker stimulatesglucose metabolism in the inner part. Flicker also increases the blood flow rate inboth retina and optic nerve head. Nitric oxide seems to play a role in mediating theflicker-induced flow changes and in maintaining the basal vascular tone in the opticnerve head in cats. Substantial species differences were observed.