PROTECTION AGAINST LIGHT-INDUCED RETINAL DEGENERATION BY AN INHIBITOROF NO SYNTHASE

THE existence of nitric oxide synthase (NOS) in retinal rod outer segm ents and pigmented epithelial cells suggests that NO in excess could i mpair the interaction between these cells, resulting in photoreceptor degeneration. To test this hypothesis, N-G-nitro-L-arginine methyl est er (L-NAME), an NOS inhibitor, was intraperitoneally injected daily in to rats subjected to constant illumination for 7 days in order to dest roy their photoreceptors. By measuring photoreceptor nuclear layer thi cknesses, we found that L-NAME partially protects (by up to 35%) again st the degeneration of photoreceptors and acts to maintain their organ ization. Thus NO may be involved in the process by which photoreceptor degeneration results from constant illumination of the retina.