Histopathological evaluation of melatonin as a protective agent in heart injury induced by radiation in a rat model

Introduction: Melatonin is a hormone which is known to be a powerful cardioprotective agent due to its free radical-scavenging properties. This study was carried out to evaluate whether melatonin administration prior to irradiation would have a protective effect on cardiac histopathological changes in an experimental rat model.

Methods: Rats were divided into four groups. Single dose of 18 Gy radiation and sham radiation exposure were used in related groups. 50mg/kg dose of melatonin were injected intraperitonally 15 min prior to radiation exposure. Analyses and assessments were performed 6 months after radiation exposure.

Results: Severe myocardial fibrosis was observed prominently in three regions: the apex, tips of papillary muscles and adjacent to the atrioventricular valves. Inflammation was found to be more in irradiated groups. Increased inflammation and fibrosis were in concordance. The number of mast cells was found to be decreased in irradiated groups. Myocyte necrosis and fibrosis were diminished with melatonin while vasculitis was prevented.

Conclusions: Elementary pathological lesions of radiation-induced heart disease (RIHD) are fibrosis, vascular damage, vasculitis and myocyte necrosis. Development of vasculitis was prevented by the use of melatonin. Fibrosis and necrosis were prominently decreased. Prevention of RIHD with the use of melatonin at the long term is encouraging according to the histopathological results.