We propose to study the metabolism of phospholipids and arachidonic acid in the endothelium, stroma and epithelium of the rabbit cornea. We will explore the factors that modulate phospholipid metabolism cell membranes in the cornea with both in vivo and in vitro experiments. We will test the hypothesis that corneal innervation regulates the metabolism of phospholipids in epithelial cellular membranes. Our plan proposes to evaluate neural influences by determining the effect of autonomic and sensory deafferentation and of nerve stimulation on corneal lipid metabolism. Radiolabeled precursors will be injected in the anterior chamber or will be placed in contact with the cornea through an attached perfusion chamber. The synthesis and turnover of membrane phospholipids, particularly of phosphatidylinositol and phosphatidic acid, will be studied. The enhanced turnover of these phospholipids upon stimulation of surface receptors in other tissues leads to calcium ionization and physiological responses. The release of arachidonic acid will be determined as well as the factors involved in regulating its free concentration in the cornea. This fatty acid must be released from membrane lipids prior to its conversion into prostaglandins and other biologically active compounds. Among the effects of these compounds is the mediation of inflammation. Hence, the acylation and hydrolysis of arachidonate-containing lipids will be examined and the fate of radiolabeled arachidonic acid will be assessed. The synthesis of the major metabolites from the cyclooxygenase and lipoxygenase pathways will be studied. Phospholipid dynamics during repair and wound healing will be explored in vivo. Different wound healing models will be compared to evaluate membrane lipid formation and inflammation-promoting prostaglandins accumulation as a function of time after the lesion. The role of calcium and non-steroidal anti-inflammatory drugs will be studied. The breakdown of membrane lipids and their relation to the pathogenesis of corneal edema will be assessed by placing corneas in anoxia. Moreover, the effect of membrane-active drugs will be explored to enhance the rate of synthesis of membrane phospholipids and to limit its catabolism during wound healing favoring repair and limiting corneal damage.
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