Radioprotective Effect of Melatonin on Radiation-Induced Lung Injury and Lipid Peroxidation in Rats

Objective: free radicals generated by ionizing radiation attack various cellular componentssuch as lipids. the lung is a very radiosensitive organ and its damage is a doselimitingfactor in radiotherapy treatments. melatonin (mlt), the major product of the pinealgland acts as a radioprotective agent. this study aims to investigate the radioprotectiveeffects of mlt on malondialdehyde (mda) levels and histopathological changes in irradiatedlungs.materials and methods: in this experimental study, a total of 62 rats were divided intofive groups. group 1 received no mlt and radiation (unt), group 2 received oral mlt(om), group 3 received oral mlt and their thoracic areas were irradiated with 18 gy (omr),group 4 received mlt by intraperitoneal (i.p.) injection and their thoracic areas wereirradiated with 18 gy (ipm-r), group 5 received only 18 gy radiation in the thoracic area(r). following radiotherapy, half of the animals in each group were sacrificed at 48 hoursfor evaluation of lipid peroxidation and early phase lung injuries. other animals were sacrificedin the eighth week of the experiment for evaluation of the presence of late phaseradiation induced lung injuries.results: pre-treatment of rats with either i.p injection (p < 0.05) and oral administration ofmlt (p < 0.001) significantly reduced mda levels in red blood cell (rbc) samples comparedto the r group. furthermore, i.p. injection of mlt decreased mda levels in plasmaand tissue (p < 0.05). in the early phase of lung injury, both administration of mlt significantlyincreased lymphocyte (p < 0.05) and macrophage frequency (p < 0.001). mlt reducedthe lung injury index in the lungs compared to the r group (p < 0.05).conclusion: the result of this study confirms the radioprotective effect of mlt on lipidperoxidation, and in both early and late phases of radiation induced lung injuries in ananimal model.