Retinyl palmitate in macaque retina-retinal pigment epithelium-choroid: distribution and correlation with age and...

Retinyl palmitate (RP) and retinyl stearate (RS) are of central importance in the visual cycle because they are the major storage molecules for retinol. In some tissues (e.g. liver) the amount of vitamin A (mostly in the form of retinyl ester) is positively correlated with both the amount of alpha-tocopherol (alpha-T) and age. Furthermore, alpha-T is a noncompetitive inhibitor of the hydrolysis of RP. We measured RP, RS, alpha-T and beta+gamma-tocopherol (beta+gamma-T) as functions of distance from the foveal center (eccentricity) in the retina-RPE-choroid (NRC) of rhesus monkeys using high-pressure liquid chromatography. It was found that the central and peripheral NRC differed with respect to these parameters. The concentration (pmoles sq mm-1) of RP was higher in the central NRC than in the peripheral NRC and was at a maximum in the region of the fovea. Furthermore, although in the peripheral NRC. RP was well correlated with age and alpha-T (similar to other tissues), in the central NRC, RP per sq mm was more clearly related to photoreceptor density. These differences imply that the central NRC controls the concentration of RP within it, while the concentration of RP in the peripheral NRC is determined by its environment (e.g. nutrients available from blood) and the age of the individual.