Influence of copper and zinc on urethan-induced adenoma development in mice

Female Swiss mice were exposed to zinc chloride (0 to 500 ug/mL) or copper sulfate (0 to 200 ug/mL) in their drinking water for 15 weeks. After 3 weeks of the exposure period, the mice were administered urethan (1.5 mg/g) intraperitoneally. Urethan-induced pulmonary adenoma formation was evaluated 12 weeks later. Zinc exposure increased the number of adenomas produced but reduced the mean tumor diameter in the intermediate treatment groups, 50 and 200 ug/mL. Exposure to copper had no effect on tumor size or on tumor number. Weight gains in the mice were not affected by copper or zinc treatment, although a dose-dependent reduction in water consumption was observed with copper. Water consumption in mice exposed to zinc was elevated in one treatment group (50 ug/mL). Urethan-induced sleeping times, which reflect the rate of urethan excretion, were prolonged by zinc exposure but were unaffected by copper exposure. This finding suggests that zinc exposure impairs the elimination of urethan and enhances its carcinogenic activity, which is manifested by increased tumor formation.