The protective effect of ascorbate in retinal light damage of rats.

Cyclic light and dark-reared rats were exposed to intense visible light for various periods and then rhodopsin-measured following recovery in darkness for up to 14 days. Animals were injected with ascorbic acid or ascorbate derivatives at various doses prior to light exposure in green Plexiglas chambers. The results show that ascorbic acid administration elevates retinal ascorbate and reduces the loss of rhodopsin and photoreceptor cell nuclei resulting from intense light. When given in comparable doses, L-ascorbic acid, sodium ascorbate, and dehydroascorbate were equally effective in preserving rhodopsin. The ascorbate protective effect in the retina is also dose dependent in both cyclic light and dark-reared rats and exhibits a requirement for the L-stereoisomer of the vitamin. Ascorbic acid is effective when administered before, but not after, light exposure, suggesting that protection from light damage in the retina occurs during the light period. In some experiments, rod outer segments were isolated from rats immediately after light exposure, lipids extracted, and fatty acid composition determined. As judged by the preservation of rod outer segment docosahexaenoic acid in rats given ascorbate, the vitamin may act in an antioxidative fashion by inhibiting oxidation of membrane lipids during intense light.