Metallothionein gene expression in testicular interstitial cells and liver of rats treated with cadmium.

The rodent testes are generally more susceptible to cadmium (Cd)-induced toxicity than the liver. Cd induces predominantly testicular interstitial cell (TIC) tumors. In order to clarify the molecular mechanism underlying tissue differences in Cd sensitivity, we compared Cd-induced metallothionein (MT) gene expression, MT protein accumulation, and Cd retention in freshly isolated TICs and liver. Adult male Fischer rats received a s.c. injection of 4.0 micromol Cd/kg or vehicle and 24 h later tissues were sampled and TICs isolated. MT-I and MT-II mRNA levels were determined by slot-blot analysis followed by densitometry scanning, and MT was estimated by the Cd-heme method. Testicular lesions were not grossly or histologically observed in rats treated with 4 micromol Cd/kg. Both MT mRNA and MT (as determined by Cd-binding capacity) were constitutively present in TICs as well as the liver. TICs isolated from Cd-treated rats accumulated more Cd (4-fold), and had higher levels of MT-I (1.9-fold) and MT-II (1.4-fold) mRNAs over control, but contained less MT (30% decrease) than TICs isolated from control animals. Cd exposure substantially increased hepatic Cd content (6000-fold), MT (58-fold), and MT-I mRNA (5.3-fold), but did not increase MT-II mRNA. Thus, our findings indicate that, although low-dose Cd exposure results in increases of MT mRNA in TICs it does not enhance MT synthesis within these cells. The inability to induce the metal-detoxicating MT-protein, in response to Cd, might account for higher susceptibility of testes to Cd toxicity and carcinogenesis relative to liver.