The effect of arsenic on urethan-induced adenoma formation in Swiss mice.

Female Swiss mice were exposed to sodium arsenite or sodium aresenate in the drinking water for 15 weeks at concentrations ranging from 0 to 100 micrograms/mL arsenic content. After three weeks of the 15 week exposure period, the mice were administered urethan (1.5 mg/g) intraperitoneally. Pulmonary adenoma formation was evaluated 12 weeks later. Arsenic exposure produced a protective effect with respect to tumor development. Both forms of arsenic reduced the size and number of pulmonary adenomas observed per mouse. In addition, urethan-induced sleeping times which reflect the rate of urethan metabolism or excretion remained unchanged. This suggests that arsenic exposure does not alter urethan excretion and is not a factor influencing subsequent adenoma formation of these levels of exposure.