Synthesis of leukotrienes in frog retina and retinal pigment epithelium

Leukotrienes (LT) were identified in the intact frog (Rana pipiens) retinal pigment epithelium (RPE), retina, isolated rod outer segments (ROS), and ROS-free (neuronal) retina. Levels of endogenous LTC4 were measured by radioimmunoassay (RIA) in both unpurified incubation medium and in incubation medium purified by reverse-phase high-performance liquid chromatography (HPLC). The purified LTC4 exhibited characteristic ultraviolet absorption spectrum with lambda max at 280 nm. The Ca2+ ionophore A23187 (10 microM) increased LTC4 production in intact and ROS-free retina and RPE but had no effect on LTC4 levels in isolated ROS. This lack of effect suggests that LTC4 is present but not synthesized in ROS. Synthesis of radiolabeled LTC4 in frog retina and RPE prelabeled in vivo by intravitreal injection of [1-14C]arachidonic acid (20:4, n-6) provided an additional verification of the presence of LTC4 in these tissues. The physiological significance of the presence of these biologically active derivatives of arachidonic acid in photoreceptor cells and retinal pigment epithelium may be related to the interactions between these cells, consisting of photoreceptor membrane shedding and phagocytosis.