Immunohistochemical localization of metallothionein in the developing teeth of cadmium-injected rats.

The ability of cadmium (Cd) to induce the synthesis of metallothionein (MT) in the developing teeth of the rat was investigated. Rats were given daily intraperitoneal injections of cadmium chloride (1.5 mg Cd/kg) for 7 days. The induction of MT synthesis in incisor teeth after Cd treatment was investigated immunohistochemically using a polyclonal antibody to MT. Immunoreactivity to MT was observed in the papillary layer of epithelial cells of the secretory zone, in one layer of epithelial cells of the presecretory zone and within ameloblasts of the postsecretory zone. Normal control rats did not exhibit MT staining. These results indicate that Cd induces MT synthesis within specific epithelial cells of the enamel organ of the rat. It is proposed that these findings demonstrate an adaptive cellular mechanism that protects these cells from cadmium toxicity.