Synthesis of leukotrienes in frog retina and retinal pigment epithelium

Abstract

Leukotrienes (LT) were identified in the intact frog (Rana pipiens) retinalpigment epithelium (RPE), retina, isolated rod outersegments (ROS), and ROS-free (neuronal) retina. Levels of endogenous LTC₄ were measured by radioimmunoassay (RIA) in both unpurified by reverse-phase high-performance liquid chromatography (HPLC). The purified LTC₄ exhibited characteristic ultraviolet absorption spectrum with λ_max at 280 nm. The Ca²⁺ ionophore A23187 (10 μM) 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 notsynthesized 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 photoreceptorcells and retinal pigment epitelium may be related to the interactions between these cells, consisting of photoreceptor membrane shedding and phagocytosis.