Distribution of membrane phospholipids in the rabbit uvea

Since the uveal tract becomes involved in inflammatory disorders, which are known to affect lipid metabolism, we studied normal membrane phospholipids (PLs) in order to (1) determine baseline PL profiles of the iris, ciliary body, and choroid, and (2) compare and contrast PL profiles of the uveal tissues.

Iris, ciliary body and choroid tissues were isolated from rabbit eyes (n = 30) and extracted with chloroform-methanol using a modified Folch procedure. Quantitative tissue PL profiles were obtained using 31P nuclear magnetic resonance.

Fourteen PLs were detected and quantitated in all three uveal tissues among which was one unidentified PL at -0.17 ppm. The five major PLs in the iris, ciliary body and choroid, respectively, have the following PL composition (mole percent of total phosphorus): ethanolamine plasmalogen 14.58, 15.07, 16.52; phosphatidylethanolamine 13.10, 12.40, 9.23; phosphatidylserine 11.24, 10.27, 12.13; sphingomyelin (SM) 11.10, 11.97, 18.21; and phosphatidylcholine (PC) 36.61, 36.70, 29.88. Additionally, lysophosphatidic acid, phosphatidic acid, lysophosphatidylcholine, phosphatidylinositol, and PC plasmalogen or alkacyl PC were detected in all tissues. Sphingosylphosphorylcholine also was detected in the ciliary body and choroid. Lysophosphatidylethanolamine was detected in the choroid. In addition, 42 PL metabolic indexes were calculated from these data, which permitted pathway-specific lipid analyses.

This study establishes baseline PL profiles of the uveal tract tissues and will permit comparisons with tissues from eyes with inflammatory disorders. The PL concentrations in conjunction with the indexes demonstrate that overall the choroid has membranes that are less permeable to ion translocation than either the iris or the ciliary body, although there are compensatory concentration changes between the SM and PC components among these three tissues.