Effect of mercury on glutathione and thyroid hormones

Abstract

In our previous work (Sin, et al 1983), oral administration of mice with mercuric chloride (HgCl2) or mercuric sulphide (HgS) showed that the low solubility of HgS would result in a lower absorption rate of mercury via the gastrointestinal tract as compared to the HgCl2. Therefore, the biological effects of these two mercuric compounds towards animals appear to vary according to these levels of tissue accumulation of the absorbed ionic mercury (Sin, et al 1989). Friberg and Vostal (1974) reported that the absorbed ionic mercury forms complexes with SH groups in the tissues of the body. This leads to the suggestion that cysteine alone might be a critical factor in the control of mercury deposition in body tissues (Thomas and O'Tuama, 1979). However, cysteine is also used for synthesis of glutathione (GSH) which, in turn, may serve as a reservoir of cysteine (Higashi, et al 1977). Sulfoxidation of the cysteine will lead to the formation of inorganic sulphate (Stipanuk, 1986). On the other hand, thyroid hormones (T3 and T4) are also known to conjugate with glucuronide or sulphate (Roche and Michel, 1960, Tan and Wong, 1989) for biliary or urinary excretion. If that is the case, it would be interesting to study the changes of glutathione and thyroid hormones in animals treated with mercuric compounds of different solubilities.