Pulmonary toxicity caused by acute exposure to mercury vapor is enhanced in metallothionein-null mice

This study examined the protective role of metallothionein (MT) against pulmonary damage caused by acute exposure to metallic mercury (Hg 0) vapor using MT-null and wild-type mice. Both strains of mice were exposed to Hg 0 at 6.6 to 7.5 mg m 3 for 4 hr each day for 3 consecutive days. This dosing protocol was lethal to over 60% of MT-null mice but did not kill any wild-type mice. More severe pulmonary damage was found by histopathological observation in MT-null mice than in wildtype mice. MT levels in the lung were elevated in wild-type mice after Hg 0 vapor exposure, and gel filtration of the lung cytosol revealed that most of the mercury was associated with MT. In MT-null mice, MT levels were below the limit of detection (0.2 μg/g tissue) for the MT assay even after exposure. After exposure to Hg 0 vapor for 3 consecutive days, the pulmonary mercury levels in wild-type mice were significantly higher than in MT-null mice. These findings suggest that MT plays a protective role against the acute pulmonary toxicity of Hg 0 vapor.