title: Vitamin A in human eyes: amount, distribution, and composition.
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 +/- 4.3 nmol/eye (n = 28), or 10.4 +/- 7.1 microgram/gm (n = 27). There was no evidence for significant losses during the interval between death and enucleation or during subsequent storage at 4 degrees 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, we estimated that the amount of vitamin A in the RPE-Ch of fully dark-adapted eyes would represent 2.5 mole 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 isomer was formed under these conditions.
mesh_terms: D002829:Choroid / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D004951:Esterification; D005123:Eye / Q000032:analysis*; D006801:Humans; D007536:Isomerism; D010857:Pigment Epithelium of Eye / Q000032:analysis; D012160:Retina / Q000032:analysis; D012243:Rhodopsin / Q000032:analysis; D014801:Vitamin A / Q000031:analogs & derivatives / Q000032:analysis*
chemical_list: D014801:Vitamin A; D012243:Rhodopsin