In this study, the toxic effects of subacute 2,3,7,8- tetrachlorodibenzo-p-dioxin on brain and heart tissues and the protection of melatonin against these effects in rats were investigated.

A total of 28 male Sprague-Dawley rats weighing between 230-250 g were used in the present study and divided into groups as seven rats in each group. The experimental period was 30 days. Animals were divided into four groups, as control group, melatonin group (5 mg/kg dose of melatonin was given), TCDD group (500 ng/kg TCDD was given), TCDD+melatonin group (500 ng/kg TCDD and 5 mg/kg melatonin were given simultaneously). After 24 hours of the last drug application, rats were decapitated and their brain and heart tissues were removed for biochemical analysis. The tissue malondialdehyde (MDA), reduced glutathione (GSH) levels and catalase (CAT) activities were measured spectrophotometrically. Heart tissue was also examined histopathologically.

MDA levels of brain and heart tissues were determined to increase in TCDD groups (P<0.05) and simultaneous application of melatonin to reduce this value in TCDD+melatonin group. GSH levels in both brain and heart tissues were observed to be decreased in TCDD groups compared to control groups while melatonin administration did not provide statistical difference in TCDD+melatonin group (P>0.05). No change in CAT activities was observed in either brain and heart tissues in all groups (P>0.05). In addition TCDD was observed to cause histopathological changes in heart tissue and melatonin to reduce these changes in TCDD+melatonin group.

Consequently, this study clearly indicated that TCDD induced toxicity by increasing the formation of free radicals in brain and hearth tissues, while melatonin might provide improvements on oxidative and histopathological damage.