Biological role of melatonin on retinal rhodopsin. an experimental study

ABSTRACT

Melatonin plays a significant role in enhancing the immune system, preventing cancer by protecting DNA, protecting human white blood cells from radiation and has a direct protective effect on the heart and the circulatory system in general. It also has anticataract function and reduces lipid peroxidation. In the present work, the effect of treatment with different doses of exogenous melatonin on the biophysical characteristics of retinal rhodopsin at different periods was studied using different techniques. New Zealand white rabbits were grouped into five sets [I, II, III, IV and V]. Animals of set I was used as control. Sets II, III, IV and V were injected daily with melatonin by doses of 10, 100, 500 and 1000 mu g, respectively, for the periods of 24 hr, one, three and five months. After the studied periods, the retinas were separated and rhodopsin was extracted, then the following measurements were carried out Measurement of the uv-visible absorption spectrum, estimation of total protein content and determination of the amino acid pattern. The data indicated that melatonin at low doses [10,100 mug] significantly affects both total protein and the opsin part rather than the high doses [500, 1000 mu g]. Low doses of melatonin will preserve all the amino acids, which are the most important for rhodopsin structure and characteristics. Melatonin at physiological doses - similar to those secreted in the body- is useful for the eye but at high doses melatonin may change the structure of rhodopsin molecule