Acute toxicity of cadmium in rats with or without cadmium pretreatment

The acute toxicity of cadmium (Cd) in male rats was examined with or without Cd pretreatment. Firstly, the metallothionein (MT) contents in the liver and kidney after Cd exposure (2.0 mg/kg, i.v.) were determined. The MT contents in the liver increased immediately to a peak (36.0 +/- 5.5 n mol/g wet tissue) 2 days after Cd exposure and were 55-fold higher than that at 0 day (0.64 +/- 0.25 n mol/g wet tissue). On the other hand, the MT contents in the kidney increased slightly but steadily for 14 days after Cd exposure. In the study for comparison of Cd-induced toxicity, the LD50 value of the Cd-pretreatment group (Group II) was approximately 2-fold higher than that of the non-pretreatment group (Group I). In microscopic findings, differences between rats in Group I and Group II were recognized in the kidney. Cytoplasmic vacuolation of the proximal tubular epithelium in the kidney was observed in Group I, while degeneration or coagulative necrosis in the proximal tubular epithelium was observed in some rats in Group II in addition to the cytoplasmic vacuolation. Because the toxic changes other than in the kidney in Group II were almost equal to or less than that in Group I, in spite of the doubled dosage of Cd, the toxic effects of Cd, except on the kidneys, were considered to be reduced by the pretreatment with Cd.