To study the effect of dietary fatty acid on the colon tumorigenesis induced by methyl nitrosourea in rats, male SD rats were fed five semi_synthetic diets composed of different proportions of beef tallow, soybean oil, alkana oil, corn oil and fish oil for 180 days. The experimental groups were injected with a solution of methyl nitrosourea in phosphate buffer intraperitoneally once a week for six weeks. The control groups were injected with phosphate buffer solution only. The incidence of colon cancer, the avergage volume of the tumors, proliferation cell nuclear antigen, cell kinetics, membrane lipid fluidity, alkaline phosphatase activities and the content of prostaglandin E-2 in colon mucosa and the fatty acid of testis pad fat were measured at the end of the experiment. The results showed that the incidence of colon cancer and the average volume of tumors in animals fed with diets composed mainly of beef tallow, soybean oil or alkana oil were significantly higher than those that were fed fish oil. The most effective anticancer diet in our study contained saturated fatty acid, monounsaturated fatty acid and polyunsaturated fatty acid of fish oil in the proportion of 13.9%, 16 4% and 68.8% respectively. Inhibition of colon tumorigenesis appeared to be related to the regulation of membrane lipid fluidity, and a decrease in the proliferation of cell nuclear antigen in colon cells. In addition, a decrease was noted in the number of cells in S phase and alkaline phosphatase activity, along with inhibition of arachidonic acid products and a corresponding decrease in the amount of prostaglandin E-2.
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