Effects of selenium on azo dye hepatocarcinogenesis

Groups of male Sprague--Dawley rats were maintained on three regimens: I. basal diet plus 0.05% 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB), II. same as I plus 6 ppm selenium (Na2SeO3) in the drinking water, and III. same as I plus 6 ppm selenium added to the diet in the form of a high selenium yeast. The 3'-MeDAB was incorporated in the diet for 8 weeks and then removed. The selenium supplements in Groups II and III were continued for an additional 4 weeks. At sacrifice the liver tumor incidence from was ascertained as the ratio of animals with tumors/total number of surviving animals per group. Selenium reduced the incidence from 92% (11/12) in the Group I control, to 46% (7/15) in Group II and to 64% (9/14) in Group III.