DIETARY N-3 FATTY-ACIDS DO NOT AFFECT INDUCTION OF HA-RAS MUTATIONS IN MAMMARY-GLANDS OF NMU-TREATED RATS

The purpose of this study was to determine whether dietary n-3 polyunsaturates (PUFA) can affect the frequency of N-nitrosomethylurea (NMU)-induced Ha-ras mutations in virgin female F344 rat mammary glands. Two groups of 15 rats each were fed isocaloric diets containing either 23% w/w corn oil or corn oil plus menhaden oil (1:1) at starting 14 d before NMU administration (day 50 of age) and continuing for 13 wk. Mammary gland samples were taken serially at 3, 5, 9, and 13 wk post-NMU treatment. Total cellular DNA was isolated and analyzed by a newly devised enriched amplification procedure that involves predigestion of normal Ha-ras alleles at codon 12, amplification of the mutant alleles, and restriction fragment length polymorphism analysis. Selective amplification enabled the detection of Ha-ras mutations as early as 3 wk post-NMU treatment. Approximately 40-50% of all glands and 75% of all rats tested had the Ha-ras codon 12 mutation. No significant differences were found between the two dietary groups at any time point, indicating that the mammary tumor-inhibiting effect of n-3 PUFA is probably not exerted at the level of the Ha-ras activation step in NMU tumorigenesis.