Light exposure stimulates arachidonic acid metabolism in intact rat retina and isolated rod outer segments

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Abstract
This paper presents evidence that short-term exposure to light increases synthesis of hydroxyei-cosatetraenoic acid (HETE) and prostaglandin D2 (PGD2) and stimulates the uptake and metabolism of 20∶4 in phospholipids and triacylglycerols in rat retina. There was a time-dependent increase in incorporation of 1-14C-20∶4 into glycerolipids in both dark-adapted and light-exposed groups. Exposure to light for 15 or 30 min enhanced the acylation of 20∶4 into phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and triacylglycerols. In the light-exposed groups there was a large increase in the conversion of 20∶4 to leukotriene B4, two diHETEs, 5-HETE, 15-HETE, and PGD2. The stimulation of HETE synthesis by light could be due to early stages of light-induced lipid peroxidation in visual cells. To examine this, we studied peroxidation of 20∶4 in isolated rod outer segments (ROS). There was more oxidation of 20∶4 in light-exposed ROS, as compared to ROS incubated in the dark. Vitamin E and nordihydroguaiaretic acid inhibited the light-induced formation of some of these products. The data indicate that photo-oxidation of 20∶4 in ROS is accompanied by enzymatic oxygenation that is stimulated by light. Increased production of HETEs and PGD2 may be a consequence of the light-induced stimulation of the metabolism of 20∶4 in membrane phospholipids in the retina.