Lipid mediators in the rat retina: Light exposure and trauma elicit leukotriene B₄ release in vitro

Abstract

Light exposure not only elicits a visual response but may also alter functional and structural characteristics of the retina. Furthermore, light exposure can lead to reversible or irreversible lesions of photoreceptors and pigment epithelium. Previous studies in our laboratory have shown that light liberates arachidonic acid from retinal membrane phospholipids mainly by activating the phospholipase A₂. In this study we show that light and trauma elicit the synthesis of leukotriene B₄ in the isolated rat retina in vitro. Male albino rats were dark adapted for 36 h, isolated retinae were taken, incubated and exposed a) either to darkness or to 5,000 lux of cool white fluorescent light for 5, 10 or 15 min at 37°C, b) either to darkness or to 5,000 lux of cool white fluorescent light for 15 min at 0°C or c) either to darkness or to 5,000 lux of cool white fluorescent light for 15 min at 37°C with a 5-lipoxygenase inhibitor (zileuton). Eicosanoids were extracted and leukotriene B₄ levels were determined by radioimmunoassay. Removal of retinae and incubation in darkness caused a significant rise in leukotriene B₄ levels with increasing incubation time. This rise was further augmented significantly after light exposure. The leukotriene B₄ levels obtained when incubating the retinae either at 0°C or with the lipoxygenase inhibitor zileuton as well as the high specificity of the radioimmunoassay indicate that the light- and trauma-elicited synthesis of leukotriene B₄ is mediated by activating the 5-lipoxygenase. Leukotriene B₄ may be involved, at least in part, in the pathogenesis of retinal diseases including light damage.

Key Words:

• arachidonic acid
• eicosanoids
• leukotrienes
• retinal light damage
• rat retina