Alterations in urethan-induced adenoma formation in mice exposed to selenium and nickel.

Female Swiss mice were exposed to sodium selenite (3 micrograms/ml selenium content) and nickelous chloride (100 micrograms/ml nickel content) in the drinking water on alternate days for 15 weeks. After 3 weeks of metal exposure, the mice were administered urethan (1.5 mg/g) intraperitoneally. Pulmonary adenoma formation was evaluated 12 weeks later. Selenium exposure did not alter the tumor incidence (P = 0.059) or the tumour size (P = 0.98). Nickel exposure did not affect the tumour incidence (P = 0.25), but increased the average tumour size (P = 0.0025). Combined selenium and nickel exposure resulted in significant interactions associated with tumour size (P = 0.00075) and tumour number (P = 0.045). Urethan-induced sleeping times were reduced by selenium exposure (P = 0.0049), but were unaffected by nickel exposure (P = 0.99). Combined metal exposure did not influence urethan-induced sleeping times (P = 0.48).