Distribution of cadmium and metallothionein in CdCl2-exposed rat kidney: Relationship with apoptosis and regeneration

Male Sprague-Dawley rats were injected subcutaneously with 0.6 mg cadmium/k g bodyweight per day for 6 weeks. In each week of exposure, rats were kille d and the localization of cadmium and metallothionein in the kidney was stu died by histochemical and immunohistochemical methods. Although cadmium was localized throughout the proximal tubules during exposure, apoptosis and s ubsequent regeneration were observed mainly in the straight portion of the proximal tubules after 4 weeks of exposure. The distribution of tubular inj ury may thus not necessarily coincide with that of cadmium. Expression of m etallothionein was also detected in the cytoplasm and nuclei of the convolu ted and the straight portion of the proximal tubules, but the latter became positive in accordance with apoptosis and regeneration. These results sugg est a close relationship between metallothionein distribution and tubular c ell regeneration.