BALB/c Mice Fed Milk or Beef Protein: Differences in Response to 1,2-Dimethylhydrazine Carcinogenesis23

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Abstract
The development of 1.2-dimethylhydrazine (DMH)-induced colon tumors and immune responses were investigated in male BALB/c mice fed six different equicaloric diets. Milk or beef at a low (11%) or high (33%) level supplied the dietary protein. and com oil (primarily) at a low (5%) or high (30%) level supplied the fat. Eleven weekly injections of DMH (at 20 mg/kg mouse) or saline were administered. At 59 weeks of age. the milk-fed mice had a significantly higher (P≤.05) colon tumor incidence than the beef-fed mice. 67 and 16%. respectively. Tumor volume and colon weight in the milk-fed mice were also significantly greater. Low natural killer cell activity against [125I]5- iodo-2′-deoxyuridine-labeled colon tumor celis and high serum blocking of antitumor cell activity were observed in the milk-fed mice. These mice also exhibited higher T -lymphocyte cytotoxicity against colon tumor cells. These results differ from those of our previous studies and those of numerous epidemiologic investigations.