VITAMIN-A IN HUMAN EYES - AMOUNT, DISTRIBUTION, AND COMPOSITION

  • 1 January 1982
    • journal article
    • research article
    • Vol. 22  (6) , 706-714
Abstract
The amount, distribution and composition of vitamin A stored in the eyes of 29 postmortem donors was determined by a combination of techniques, including high-pressure liquid chromatography. The vitamin A concentration in the pigment epithelium-choroid (RPE-Ch) was the highest observed for human non-liver tissue and amounted to 7.9 .+-. 4.5 nmol/eye (n = 28) or 10.4 .+-. 7.1 .mu.g/g (n = 27). There was no evidence for significant losses during the interval between death and enucleation or during subsequent storage at 4.degree. C. The vitamin A extracted from the retina was 15.3% of that in the corresponding RPE-Ch. By measuring rhodopsin regeneration in retinal homogenates incubated with 11-cis retinal, the amount of vitamin A in the RPE-Ch of fully dark-adapted eyes would represent 2.5 mol equivalents of the retinal rhodopsin, a value similar to that found in the frog. A preponderance of the vitamin A in the eye was esterified (98.3% in the RPE-Ch, 79.3% in the retina) and consisted principally of stearate and palmitate in the ratio of 1:4.8. A small amount of oleate was also detected. The ratio of 11-cis isomer over the all-trans averaged 1.52 .+-. 0.48 (n = 11). Variable, usually small proportions of 13-cis retinyl esters were also present. Intact RPE-Ch or isolated RPE cells esterified exogenous all-trans-3H2-retinol to the same fatty acids in roughly the same proportions as in the endogenous stores. The all-trans configuration was mainly retained during uptake and esterification, although some isomerization to 13-cis also occurred. No 11-cis was formed under these conditions.