Effect of mercury intoxication on thyroid function and blood cholesterol

¯Abstract Background: ‌ Mercury is a heavy metal and transition element in periodic table that has many uses in industries, agriculture and medicine. This element can enter the body through different routs including food materials, ventilation and skin. Objective: To investigate the short and long term effect of mercury on thyroid hormone in the sera from rats. Methods: Mercuric chloride in doses of 3 mg/kg (short term or 10-day injection) and 1 mg/kg (long term or 45- and 60-day injection) was injected intraperitoneally into three test groups of rats (n=5). Following each period of injections, the blood samples were collected for T3, T4, TSH and T3 uptake measurements. Blood cholesterol level was measured simultaneously for monitoring cholesterol changes. Findings: After the 10-day injection, values for T3, T4 and TSH in test group were decreased 29, 18 and 30 percent, respectively, compared to control group (P<0.04). T3 uptake was increased 23 percent (P<0.04). The 45-day injection caused a decrease in the levels of T3, T4, and TSH as 30, 16 and 40 percent, respectively. T3 uptake and blood cholesterol levels were increased 25 and 8 percent respectively. Following the 60-day injection, the levels of T3, T4, and TSH in test group were decreased 51, 28 and 44 percent, respectively. T3 uptake and blood cholesterol levels were increased 22 and 11 percent respectively (P<0.05). Conclusion: Based on data obtained from current study, it seems that mercury chloride can lead to hypothyroidism and causes an increase in blood cholesterol level. Direct toxic effect of mercury on liver leads to low protein synthesis and may contribute to increase the serum concentration of T3 uptake. Higher level of cholesterol may be attributable to resulting hypothyroidism, which in turn lowers T4 and T3 concentrations.