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Cadmium Carcinogenesis in Male Wistar [Crl:(WI)BR] Rats: Dose-Response Analysis of Effects of Zinc on Tumor Induction in the Prostate, in the Testes, and at the Injection Site

Inorganic Carcinogenesis and Tumor Pathology and Pathogenesis Sections, Laboratory of Comparative Carcinogenesis, Division of Cancer Etiology, National Cancer Institute, Frederick, Maryland [M. P. W., S. R., R. M. B., L. A. P.]; Data Management Services, Frederick Cancer Research Facility, Frederick, Maryland [C. W. R.]; and Microbiological Associates, Inc., Bethesda, Maryland [D. E. D., M. L. W., J. R. H.]

The ability of zinc acetate to modify the carcinogenic effects of CdCl₂ in male Wistar [Crl:(WI)BR] rats was studied over a 2-year period. Groups of rats received a single s.c. injection of Cd (30.0 µmol/kg) in the dorsal thoracic midline or i.m. in the right thigh at time 0. Zinc was given in three separate s.c. doses of 0.1, 0.3, or 1.0 mmol/kg (at -6, 0, and +18 h relative to cadmium) in the lumbosacral area or p.o. at 100 ppm in the drinking water (-2 to +100 weeks). Cadmium treatments (s.c.) resulted in the appearance of tumors at the injection site and in the testes. The incidence of s.c. injection site tumors (mostly mixed sarcomas) was markedly reduced by high dose (1.0 mmol/kg) s.c. zinc (50% reduction) and was almost abolished by p.o. zinc (92% reduction). Testicular tumors (mostly Leydig cell adenomas) induced by s.c. cadmium were reduced in a dose-related fashion by zinc and were found to be highly dependent on the ability of zinc to prevent the chronic degenerative effects of cadmium in the testes. Oral zinc had no effect on s.c. cadmium-induced testicular tumors, while i.m. cadmium alone did not induce these tumors. In rats in which s.c. cadmium-induced testicular tumors and chronic degenerative effects were prevented by zinc (1.0 mmol/kg, s.c.), a marked elevation in prostatic tumors (exclusively adenomas) occurred (control, 9.6%; cadmium plus high zinc, 29.6%). Cadmium given i.m., which did not result in testicular tumors or degeneration, also induced an elevated incidence (42.3%) of prostatic tumors, again indicating a dependence on testicular function. Prostatic tumor incidence was also significantly elevated (25.0%) in rats receiving 1.0 mmol/kg zinc, s.c., in combination with i.m. cadmium. These results indicate that zinc inhibition of cadmium carcinogenesis is a complex phenomenon, depending not only on dose and route but also on the target site in question.

¹ To whom requests for reprints should be addressed, at Laboratory of Comparative Carcinogenesis, NCI-FCRF, Building 538, Room 205E, Frederick, MD 21701.

² Present address: Laboratory of Comparative Carcinogenesis, NCI-FCRF, Frederick, MD 21701.

³ Present address: Division of Chemical Toxicology, NCTR, Building 15, Jefferson, AR 27079.

⁴ Present address: Biological Carcinogenesis Development Program, Program Resources, Inc., NCI-FCRF, Frederick, MD 21701.

Received 11/16/88. Revised 4/ 6/89. Accepted 5/ 3/89.

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