L-selenomethionine (Sigma, St. Louis, MO) was mixed into the diet (NIH-07; Harlan Teklad) using a Blend-Master Model B Lab Blender (Patterson-Kelly, East Stroudsburg, PA). A vehicle of D(+) sucrose (Sigma) was used at a dietary concentration of 10 g/kg diet (1% w/w) to achieve final selenium concentrations of 1.5 or 3.0 mg/kg diet. The control diets contained the same amount of sucrose and 0.31 mg/kg selenium, while the selenium concentration in tap water provided to the animals varied between undetectable and 6.1 ppb. The diet concentrations and form of selenium were selected based on previous experiments with rat models of prostatic carcinogenesis [18 (link), 23 (link)]. Furthermore, L-selenomethionine was used in the SELECT trial [34 (link)] and is regarded as the dominant form of selenium in human foods. The dose levels of selenomethionine were approximately 40% and 80%, respectively, of the maximally tolerated doses identified previously in selenium-adequate Wistar rats. These levels had been reported to increase mean plasma selenium levels in the rats by 9% and 17%, respectively [18 (link)].