Effect of Semisynthetic Diets Containing Various Amounts of Corn Oil upon Development of DMBA-Induced Mammary Cancer

Abstract

To ascertain the effect of fat-content in diet on the development of breast cancer, the semisynthetic diets containing corn oil (polyunsaturated fatty acids; more than 80%) in the weight percentages of 0,8 or 40 were prepared and 141 young adult Sprague-Dawley females were used for the following experimental designs. In the first group, the uptake and clearance of labeled DMBA within the mammary fatty pads of 20 rats administered by fat-free and 40%corn oil diets, respectively, at the ages of 45-87 days were observed in 3 days after the intravenous injection of carcinogen. In the second group,90 rats (a-subgroup) were intubated by 10mg of DMBA twice on the ages of 56 and 59 days, and 31 rats (b-subgroup) never received DMBA. The animals of b-subgroup were fed on fat-free,8% corn oil and 40% corn oil diets, respectively, at the ages of 70-100 or -115 days, and they were finally sacrificed either for the determination of serum prolactin and estrogens or for the analysis of fatty acid compositions within the mammary fatty pads. The effective number of rats in a-subgroup were fed on 3kinds of the above-mentioned semisynthetic diets, respectively, at the ages of 90-150 days, and they were applied to the observations on the developments of mammary cancers, endocrinologic states of these cancer-bearers and fatty acid compositions of these mammary tumor phospholipids.
In group II a, the averages of caloric intake were 52.4,52.2 and 50.3 Cal/rat/day, respectively, in the fat-free,8% corn oil and 40% corn oil diet groups, and the curves of average body weight were not different from each other diet group. However, both the average number of cancer per a rat (3.2±2.2,6.5±2.5) and average weight of cancer per a rat (654.0±498.7mg,690.5±477.3mg) were much higher in the 8% and 40% corn oil diet groups, wit h compared from the fat-free diet group (1.6±0.9,331.6±226.5mg). These figures were statistically different from each other diet group (p<0.01). The endocrinologic states (serum prolactin, serum estrogens, prolactin/estrogens at the same sexual cycle and weight of the endocrine organs) of the hosts were similar in each diet groups. In the mammary tumor phospholipids, linoleic acid increased and arachidonic acid decreased in the 40% corn oil diet group, in comparison of the fat-free diet group. These deviations were statistically significant (p<0.01). In group 11b, the hormonal balances of animals seemed to be not disturbed by these semisynthetic diets, and linoleic acid within the mammary fatty pads decreased profoundly in the fat-free diet group, where any disorders from essential fatty acid deficiency could not be detected yet. In group II, the uptake and clearance of tritiated DMBA within the mammary fatty pads of the 40% corn oil diet group were not significantly different from those of the other diet groups.
In conclusion, the extremely high corn oil diet enhanced prominently the devel opment of DMBA-induced mammary cancers, especially number of cancer per an animal, without any endocrinologic and caloric alterations in these cancer-bearers. Such an enhancement might be introduced by the increased amounts of polyunsaturated fatty acids within the mammary fatty pads of the hosts and by some alterations of fatty acid composition of the tumor phospholipids.