Suppressive effect of zinc on the toxicity of mercury.

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Abstract
Hg compounds have the strongest toxicity among metals and because of the high affinity of Hg with thiol groups, they are known to affect living organisms by damaging proteins and thiol enzymes. HgCl2 gives the strongest acute toxicity and produces nephritis, neuritis and impairment of walking, besides gastrointestinal dysfunction. Male rats were given HgCl2 (0.018 mmol/kg per day) by s.c. injection and zinc acetate (3.0 mmol/kg per day) by oral administration. Hg and Zn were administered at the same time, once every 24 h for 5 days. Only 1/10 rats given Hg alone survived for 3 days and this 1 rat died on the 4th day. In the group given Mg and Zn at the same time, all 10 animals were alive on the 5th day, indicating the marked effect of Zn in suppressing the Hg toxicity. Based on such a marked Zn effect, examinations were made to see whether biosynthesis of metallothionein would occur in the presence of Zn or Hg by the incorporation of 14C-cysteine into the metallothionein fraction. High rate of incorporation of radioactivity into the metallothionein in the rat liver was observed by Zn administration but the incorporation was not so marked by Hg administration. Metallothionein induced by Zn might have some effect on lowering of Hg toxicity and then, Hg and Zn distribution in the soluble fraction was examined. In the liver, Hg bound in larger amount to high molecular fraction during single Hg administration transited to the metallothionein fraction when Zn was administered concurrently. The amount of Hg bound as Hg-thionein in the kidney after the concurrent Hg and Zn administration was about 4 times that after single Hg administration.