EFFECTS OF MELATONIN AND LIGHT ON PORPHYRIN SYNTHESIS IN THE BOVINE RETINA, PIGMENT-EPITHELIUM AND CHOROID

The quantity of porphyrin synthesized in the presence of 10(-3) M delta-aminolevulinic acid (ALA) is several times higher in the bovine pigment epithelium than in the retina. Synthesis in the retina was found to be increased by illumination, whereas synthesis in the pigment epithelium was decreased if the whole anatomical unit (retina-pigment epithelium-choroid) was cultivated together. The quantity of porphyrin synthesized in the presence of 10(-3) M ALA or 10(-6) M melatonin was different when the pigment epithelium and retina were separated. The combination 10(-3) M ALA with 10(-6) M melatonin inhibited retinal porphyrin synthesis after green light adaptation, while in the pigment epithelium green light adaptation induced porphyrin synthesis. It is postulated that the light-sensitive porphyrin-haeme synthesis of the retina-pigment epithelium-choroid functional unit may serve and modulate the synthesis of guanylate cyclase for cGMP.