The effect of melatonin on peripheral blood cells during total body irradiation in rats.

Melatonin, has been reported to participate in the regulation of a number of important physiological and pathological process. It has also the ability to protect the genetic material of hematopoietic cells of mice from damaging effects of acute total body irradiation. The objective of this study was to the potential radioprotective effects of pharmacological doses of melatonin in total body irradiated rat's peripheral blood cells. Forty adult rats were divided into 4 equal groups. Group 1 received no melatonin or irradiation (control group), while group 2 received only melatonin (5 mg/kg, i.p.). Group 3 received only total body irradiation (RT) by 5 Gy of gamma irradiation only and group 4 received RT plus melatonin (5 mg/kg, i.p., 30 min before RT). An hour and a half following RT, blood samples were taken. Leukocytes and thrombocytes number and hemoglobin levels were measured in all groups. Five mg/kg dose of melatonin significantly protected leukocytes and as well as thrombocytes number against y irradiation. There were no significant differences between Hb levels. Our results suggest that melatonin administration prior to irradiation prevented radiation damage on peripheral blood cells. Melatonin radioprotection is achieved by its ability as a scavenger for free radicals generated by ionizing radiation and acts probably as a growth factor, especially for granulocytes in bone marrow.