Changes in selenium and antioxidant status during DMBA-induced mammary carcinogenesis in rats

Female weanling Sprague-Dawley rats were used to examine the changes that occurred in selenium and antioxidant status during the development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors. Animals were fed an AIN-76 diet, modified to contain 20% fat (3:1 wt/wt, lard:corn oil) and 0.1, 0.035, 0.1, 1.0, 2.0 or 4.0 mg Se/kg diet. At wk 5, rats in groups 2-6 were administered by intragastric tube 4.32 mg of DMBA dissolved in corn oil. Control rats received corn oil only. A blood sample was removed from the tail vein and analyzed for selenium-dependent glutathione peroxidase (Se-GSHPx) and superoxide dismutase (SOD) activity at wk 5, and every 4 wk until wk 25. At the end of the experiment, rats were classified by tumor status, and each diet group was subdivided into two groups: those rats remaining free of tumors for 25 wk and those with tumors. DMBA treatment caused an initial decrease in erythrocyte SeGSHPx and SOD activity compared to untreated control rats. SeGSHPx activity in rats with tumors remained lower than controls, while SeGSHPX activity increased in rats with no tumors. These changes, however, were not associated with any changes in lipid peroxidation.