Effect of light exposure on the accumulation and depletion of retinyl ester in the chicken retina

A previous study has shown that in the cone-rich chicken retina, 11-cis retinyl ester increases with light exposure and decreases in subsequent dark adaptation. The purpose of this research is to study how light exposure (intensity and duration) determine the rate of accumulation and utilization as well as the size of this 11-cis retinyl ester pool in the chicken retina. Chickens were dark-adapted overnight before exposure to different light intensities and durations. Animals were sampled at regular time intervals. 11-cis retinal and 11-cis retinyl ester were extracted from the retina and analyzed by HPLC. An increase in light intensity from 1000 and 2000 Lux (for a 20 min exposure) increased the amount of 11-cis retinyl ester from 0.38 to 0.75 nmol/mg. An increase in the duration of light exposure from 10 to 20 min (at 2000 Lux) also increased the amount of 11-cis retinyl ester in the chicken retina (from 0.37 to 0.75 nmol/mg). This 11-cis retinyl ester pool in the chicken retina was rapidly reduced to baseline level (∼0.20 nmol/mg) upon dark adaptation. The rate of accumulation of 11-cis retinyl ester was dependent on light intensity and duration of exposure and the maximum rate was ∼0.03 nmol/mg/min. In comparison, dark adaptation was associated with a significantly higher rate of 11-cis retinyl ester depletion (∼0.05), indicating that light exposure and dark adaptation were associated with different biochemical steps of retinoid storage and utilization. Results from this study are the first to show that the size of the 11-cis retinyl ester pool, as well as the rate of its accumulation and depletion in the cone-rich chicken retina, are determined by the intensity and duration of light exposure. These data support the suggestion that a light-driven cone cycle exists in the chicken retina.