Effect of varying proportions of dietary menhaden and corn oil on experimental rat mammary tumor promotion |
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Authors: | Leonard A Cohen Jye-Yu Chen-Backlund Daniel W Sepkovic Shigeyuki Sugie |
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Affiliation: | (1) Division of Nutrition and Endocrinology, Naylor Dana Institute for Disease Prevention, American Health Foundation, 10595 Valhalla, New York;(2) Present address: Strang-Cornell Cancer Research Laboratory, New York, NY;(3) Present address: Department of Pathology, Gifu University School of Medicine, 500 Gifu City, Japan |
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Abstract: | Dose-related effects of long-chain highly unsaturated n−3 fatty acids on the development ofN-nitrosomethylurea (NMU)-induced rat mammary tumors were assessed in female F344 rats. Four test groups (36 rats/group) were
fed the following high-fat (HF) diets (23% fat, w/w): Group 1, 18% menhaden oil (MO) and 5% corn oil (CO); Group 2, 11% MO
and 11.8% CO; Group 3,5% MO and 18% CO; Group 4, CO alone. A fifth group, serving as an internal control, was fed a low-fat
diet containing 5% CO alone. Experimental diets were begun after initiation with NMU, and the experiment was terminated 31
wk later. Total tumor numbers in the five groups were 28, 16, 32, 26 and 11, respectively, indicating that the promotion phase
of NMU-induced carcinogenesis was significantly suppressed only when equal parts of CO and MO (Group 2) were fed or when CO
alone was fed at 5% (w/w). At high (Group 1) or low (Group 3) levels of MO, tumor numbers were indistinguishable from the
HF CO group (Group 4). The same pattern was observed when assessed in terms of cumulative tumor incidence and multiplicity.
However, when expressed in terms of final tumor incidence, dietary MO did not suppress tumor promotion in a statistically
significant fashion at any concentration. Animals fed MO gained weight at the same rate as those fed CO, indicating that the
presence of MO in the diet did not result in food avoidance behavior. Measurement of total serum cholesterol indicated an
inverse trend with respect to the MO content of the diet. Analysis of serum fatty acid profiles indicated that the proportion
of n−3 and n−6 polyun-saturated fatty acids (PUFA) in the serum reflected that of the diet. These results support the hypothesis
that the relative proportions of dietary n−3/n−6 fatty acids play an important role in the suppression of experimental mammary
tumorigenesis and suggest that changes in circulating cholesterol or n−3 PUFA levels, induced by dietary MO, are not directly
related to tumor development.
Presented in part at the 81st Annual Meeting of the American Association for Cancer Research, Washington, D.C., May 1990 |
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