The effect of mercury on thyroid function in sheep

The purpose of this experiment was to determine the effect of long-term low-dose administration of mercury (Hg) on thyroid function in sheep. In this experiment, 10 clinically healthy, adult, male Iranian sheep, aged approximately 1 year, were randomly allocated into the control (n=5) and mercury (Hg-)-treated (n=5) groups. Both groups were kept under identical conditions in terms of food and environment. The treatment group received mercuric chloride (5 mg/kg/day) orally for eight weeks. Blood samples were drawn between the hours of 0800 and 0900 from both groups on days 0, 14, 28, 42, 56 and 70. Thyroid function was evaluated by measuring the levels of the serum thyroid hormones, including triiodothyronine (T3), thyroxine (T4), free T3 (FT3), free T4 (FT4) and thyroid-stimulating hormone (TSH). Hepatic function was evaluated in both groups by measuring alanine aminotransferase (ALT), aspartate aminotransferase (AST),? -glutamyltransferase (GGT) and total bilirubin (TBIL). Renal function was assessed using serum creatinine (Cr) and blood urea nitrogen (BUN) levels. Serum T3 (from day 28 onwards) and serum T4, FT3, FT4 and TSH (from day 14 onwards) decreased in the Hg-treated group (p<0.05). Serum ALT, AST and GGT increased from days 42, 56 and 70, respectively, when compared to the control group (p<0.05). The concentrations of total protein and albumin decreased on day 70 and total bilirubin (TBIL), BUN and Cr levels increased on day 70 when compared to the control group (p<0.05). It was concluded that chronic administration of Hg may expose sheep to the risk of hypothyroidism.