Distribution of retinoids in different compartments of the posterior segment of the rabbit eye

Using high-performance liquid chromatography, the amounts of all-trans retinol, retinal and retinyl palmitate were measured in the following ocular tissues and fluid of the light (LA) and dark adapted (DA) rabbit: cytosol and membrane fractions of the retina (R/C and R/M), cytosol and membrane fractions of the retinal pigment epithelium (RPE/C and RPE/M), subretinal fluid collected from the inter-photoreceptor matrix (S/R) and the matrix between apical microvilli of the RPE (S/RPE). The total amount of all-trans retinol extracted from LA eyes, 2.74 nmol per eye, was ten times greater than the amount extracted from DA eyes. In the LA eye, most of the all-trans retinol was extracted from the membrane fraction of the retina (67%); in the DA eye, most of the retinol was extracted from the cytosol fraction of the retina (58%). In contrast, the DA eye yielded more all-trans retinal (9.84 nmol) than the LA eye (5.80 nmol) and most of this retinoid was recovered from the cytosol and membrane fractions of the retina. A higher amount of all-trans retinyl palmitate was recovered from the LA eye (5.88 nmol) than the DA eye (2.02 nmol). Although most of this retinyl palmitate was extracted from the cytosol fraction of the RPE (45%, LA eye), appreciable amounts were found in all other ocular compartments. The amount of retinyl palmitate in the LA eye exceeded that of the DA eye in every compartment examined in the present study, suggesting a possible important role of retinyl esters in the visual cycle.