Predisposing factors to light-induced photoreceptor cell damage: retinal changes in maturing rats

Retinal changes occurring during the period of growth and maturation of Long Evans pigmented rats were examined to obtain a better understanding of the basis for the age-dependency of light-induced photoreceptor cell damage. Susceptibility to light damage increased markedly between 30 and 60 days of age and to a lesser extent between 60 and 90 days. Although the retinal antioxidant vitamins E and C, and taurine showed a significant increase during the age-period studied, retinal lipid phosphorus and total protein increased by similar amounts indicating that the concentration of these nutrients was not changing. In contrast, rhodopsin content of the retina increased progressively by 44% between 30 and 90 days of age. While ROS length showed no appreciable change with age, rhodopsin per ROS length increased by 31% between 30 and 60 days of age and by 48% between 30 and 90 days. Determinations of ROS phospholipid to rhodopsin ratio and disks per ROS length indicated that rhodopsin did not become more concentrated in photoreceptor cells between 30 and 90 days. However, the 12% increase in ROS diameter between 30 and 90 days of age may partially account for the rhodopsin difference. These findings demonstrate an age-dependent association between greater rhodopsin per ROS length and increased susceptibility to retinal light damage. An increased metabolic demand on photoreceptor cells with greater rhodopsin may be an important factor influencing their destruction by light.