IMMUNOHISTOCHEMICAL LOCALIZATION OF METALLOTHIONEIN IN THE LIVER AND KIDNEY OF CADMIUM- OR ZINC-TREATED RATS

The localization of metallothionein (MT), a small molecular weight heavy-metal binding protein, in the liver and kidney of rats treated with either cadmium (Cd) chloride or zinc (Zn) sulfate was investigated by the indirect immunofluorescent technique. Male Wistar rats were subcutaneously injected with CdCl2 at a single dose of 3.0 mg Cd/kg body weight or 50 mg Zn/kg body weight, followed by sacrifice at 3, 6, 12 and 24 hr. For comparison, tissues were also obtained from rats treated with 1.5 mg Cd/kg body weight, 4 times a week for 6 weeks. In control rats from both short- and long-term studies the MT antigenicity was detected in the cytoplasm of hepatocytes and proximal tubular cells. A major difference in the localization of MT between the two studies was found only in the liver. The immunoreactive stain was limited to the hepatocytes around both central and interlobular veins in the long-term study compared to rather uniform localization throughout the liver in the short-term study. The intensity of immunostain of MT in both organs upon Cd or Zn treatment tended to increase with tissue concent-rations of the protein, as determined by a radioimmunoassay. Cd and Zn treatment resulted in the localization of MT in a similar manner. In particular, the number of proximal tubules with immunofluorescence increased upon an injection of Cd or Zn, and once a renal Cd level considerably increased by the repeated injections of Cd, intense stain of MT was observed not only in the proximal tubule but also the distal tubule and collecting duct. No specific immunostain was observed in the glomerulus, vascular endothelial cells and connective tissues. Although not only the cytoplasm but also the nucleus of the hepatocytes and proximal tubular cells often showed immunofluorescence, no significant change in the induction of MT between these subcellular compartments with time was found.