Significance of increase in urinary metallothionein of rats repeatedly exposed to cadmium.

Cadmium chloride was injected subcutaneously (s.c.) into female Wistar rats at a dose of 1 mg Cd/kg body weight, 5 times a week up to 10 weeks. At specified intervals, 24-h urine was collected and the excreted amounts of metallothionein (MT), cadmium, copper, zinc and several indicators of renal damage were determined. Concentrations of cadmium and MT in the livers and kidneys of rats were also determined. Both cadmium and MT in the livers and kidneys were increased upon cadmium exposure. The urinary MT excretion started to increase within a week after the start of exposure. This increased excretion preceded those of enzymes and total protein as well as histopathological abnormalities in the proximal tubular cells. After the occurrence of tubular damage that disturbs reabsorption of MT, MT in urine was drastically increased. These results indicate that urinary MT levels may be an indicator not only of cadmium exposure but also of tubular damage.