Numerous studies have consistently shown that
vegetable oils containing
linoleic acid enhance mammary
tumorigenesis more effectively than
fish oils containing eicosapentaenoic and docohexaenoic
acids. The purpose of this investigation was to study these and additional n-3 and n-6 PUFA, e.g., a-linolenic (a-LN) (18:3 n-3) and gamma-linolenic (GLA) (18:3 n-6)
acid. Different
oils were used as dietary sources of
fatty acids: corn (CO) (61% LA); blackcurrant (BCO) (44% LA, 18% GLA and 16% a-LN);
fish oil (FO) (mixed with
corn oil, 12% LA and 24% EPA + DPA + DHA). Thirty-five-day-old female Sprague-Dawley rats were divided into 5 dietary treatment groups and were allowed to feed ab libitum on one of the test diets: I. BCO (23.5%); II. CO (23.5%); III. BCO (15.5%) + FO (8%); IV. FO (20.5%) + CO (3%); and V. BCO (20.5%) + FO (3%). From 48 to 52 days of age, rats in all five groups were fed rat chow. At 50 days of age, all rats were given 5 mg DMBA by oral intubation, and 2 days later the test diets were resumed until termination of the experiment. Analysis of
tumor incidence, and multiplicity data for 5 diet groups indicated that rats fed 23.5% CO (II) exhibited enhanced mammary
tumor yields when compared to animals on the remaining 4 diets in the order II greater than I, III, V greater than IV. Since the level of fat (23.5% w/w) was similar in all 5 diets, and
body weight gain was in the order IV greater than II greater than I, the results of this study indicate that differences in
tumor yields were related to
fatty acid composition of diets. In support of this conclusion,
fatty acid profiles of RBC and
tumor phosphoglycerides reflected dietary
fatty acid composition. In groups I and II, even though
tumor levels of LA were similar, the levels of GLA, DHLA (20:3 n-6) and a-LN were higher in I compared to II, suggesting that these differences may be associated with lower yields of DMBA-induced mammary
tumors in group I. Incorporation of marine type
n-3 PUFA (EPA, DPA and DHA) in
tumor PL was greater in Group IV compared to plant type
n-3 PUFA (a-LN) in Groups I, III, and V. Since
tumor yields were the lowest in Group IV, these results suggest that incorporation of marine type
n-3 PUFA into cell membranes does not favor development of DMBA-induced mammary
tumors.