Distribution of vitamin A compounds in bovine eyes after bleaching adaptation

Abstract

A seasonal increase in the amount of bleached rhodopsin caused, in living animals, by the seasonal increase of the intensity of sunlight in the early morning before the calves are killed, was verified in the bovine eyes subjected to the present study. This was used as a means of assaying distribution and isomer composition of esterified and unesterified retinol in eyes from animals light-adapted to a different extent under environmental conditions. The progressive increase of bleached rhodopsin results in a parallel increase of all-trans-retinol in retina and of both all-trans- and 11-cis-retinyl esters in pigment epithelium. Analytical subcellular fractionation of RPE homogenate reveals that retinyl esters accumulate without an exclusive subcellular localization in nuclear, mitochondrial/lysosomal and microsomal fractions. Whatever the amount of bleached rhodopsin, only small and constant amounts of retinyl esters are found in the soluble fraction of RPE, entirely under the all-trans configuration. When a considerable portion of rhodopsin is bleached (about 70%), substantial amounts of all-trans-retinol, along with minor amounts of 11-cis-retinol, accumulate in RPE subcellular organelles. The in vitro bleaching of bovine eyes results in a distribution of retinoids between retina and RPE which appears different from that detected in eyes naturally bleached to the same extent.