High-pressure liquid chromatography of fatty acid esters of retinol isomers. Analysis of retinyl esters stored in the eye

Abstract

We have synthesized the all-trans, 13-cis, 11-cis, and 9-cis retinyl esters of some or all of the following fatty acids: caprylic (8:0), capric (10:0), lauric (12:0), myristic (14:0), palmitic (16:0), stearic (18:0), arachidic (20:0), palmitoleic (16:1), oleic (18:1), linoleic (18:2), linolenic (18:3), arachidonic (20:4), and docosahexaenoic (22:6). Mixtures of these compounds were analyzed by high-pressure liquid chromatography on an Altex 100 chromatograph. This approach has enabled us to investigate and identify both the isomeric form and fatty acid basis of the retinyl esters present in rabbit and rat ocular tissues. Dark-adapted rabbits had 11-cis and all-trans retinyl esters, whereas light-adapted albino rats had only the all-trans isomer. The fatty acids utilized for esterification were almost wholly palmitic for the rabbit, whereas both stearic and palmitic were present in the rat esters. Rabbits are similar to frogs in that a large proportion (80%) of their ocular retinyl esters occurred in large, fluorescent oil droplets in the pigment epithelium. These are absent in rats.