Ascorbate and glutathione levels in the developing normal and dystrophic rat retina: effect of intense light exposure.

Abstract

Ascorbic acid and glutathione were measured in retinas excised from normal rats reared in a cyclic light or dark environment and in dystrophic rats from the dark environment. Similar measurements were made on retinas from age matched rats exposed to intense visible light for periods of up to 24 hours. In other rats, ascorbic acid was given for various periods before exposure to intense light and the degree of photoreceptor cell death determined subsequently by rhodopsin measurements. In non-intense light treated rats ascorbate and glutathione were 12.1 nmol/retina at 20 days of age and 13.3 - 15.9 nmol/retina in 60 day old animals. In dystrophic rat retinas glutathione was 4-8% higher and ascorbate 10-20% higher than in normal dark reared rats. Although the levels of ascorbate and glutathione per retina increased during development, the molar ratios of the antioxidant materials to rhodopsin decreased by 36% and 60% in normal and dystrophic rats respectively. The levels of glutathione in young cyclic light or dark reared normals were unaffected by intense light exposure of either short (2-4 hrs) or long (24 hrs) duration. However, in both 20 and 40 day old dystrophic rats, intense light exposure resulted in a significant increase in retinal glutathione. In contrast to glutathione, retinal ascorbate decreased in normal rats exposed to intense light for 24 hrs, in an age and prior light environment dependent fashion. At ages greater than 20 days, normal rats exposed to light had significantly lower retinal ascorbate levels than their non-light exposed counterparts. The levels of ascorbate in 21-40 and 41-60 day old dark reared rat retinas were also significantly lower than in comparable intense light treated-cyclic light reared rats. In the youngest dystrophic rats whole eye ascorbate (retina, RPE, choroid and sclera) was 20-30% lower than in non-light treated rats, but in older mutant rats (41-60 day) light had no effect on the level of ascorbate in the retina. As determined by the level of rhodopsin remaining in the eye two weeks after 24 hrs light exposure, cyclic light reared rats lost 50-55% of their visual cells. However, cyclic light rats supplemented with ascorbic acid before intense light exposure lost only 30-35% of their visual cells.