Background: Mercury as one of the first known toxicants disrupts the endocrine system and thyroid gland. Aim:
Investigating the possible protective role of melatonin versus selenium in a rat model of mercury-induced thyro-toxicity.
Methods: Thirty-two male albino rats (150-165 grams) were divided randomly into four equal groups. Group I (control), Group II (intraperitoneal injection (IPI) of mercury chloride three times per week at a dose of 3 mg/kg body weight for 4 weeks), Group III (Mercuric chloride as in group II and sodium selenite at a dose of 0.5 mg/kg body weight three times per week IPI for 4 weeks), Group IV (Mercuric chloride as in group II and Melatonin at a dose of 5 mg/kg body weight IPI daily for 4 weeks). We measured serum T3 and T4, TSH, malondialdehyde (MDA), catalase, superoxide dismutase (SOD), and glutathione peroxidase (GP). We examined thyroid tissue histologically, and immunohistochemically for iNOS and PCNA.
Results: Mercury-treated groups showed a decrease in body weight, disorganized fused thyroid follicles, a decrease in the follicular diameter and colloid content, and an increase in the follicular cell height, the area percentage of iNOS, and the number of PCNA-positive nuclei. Melatonin treatment improved all these parameters significantly compared to selenium. Melatonin also significantly improved thyroid functions, increased catalase, SOD, and GP expression, and reduced MDA compared to selenium. Conclusion: we report that selenium or melatonin improved thyroid function and structural changes in mercury-treated rats. There was a more protective effect of melatonin than selenium against mercuric toxicity.