7,12-Dimethylbenz(a)anthracene-Induced and Transplantable Mammary Tumors in Female Rats Fed Geometrically Different Fats

The effect of a geometrical difference in dietary fat on mammary tumorigenesis was studied. Female Sprague-Dawley rats were fed a purified diet containing olive oil (m-monoene fat), partially hydro-genated corn oil (trans-monoene fat), or a blend of these two oils at the 10% level and received a single oral dose of 7,12-dimethylbenz(a)anthra-cene (DMBA). The difference in the fatty acid composition of dietary fats was confined to the geometry of octadecenoate with an appropriate supply of linoleic acid (2% of total energy). The latency period, the rate of the tumor incidence, and the tumor yield 20 weeks after DMBA treatment were all comparable among the three groups. The growth of transplantable mammary tumors in female Wistar rats fed 5% fat diets was also the same between trans- and cw-fat. In DMBA-treated rats, plasma eicosanoid (PGEl5 PGE2, and TXB2) levels of the trans-fat groups tended to be higher, while the concentration of 6-keto-PGFlff was comparable. The trans-fat reduced the ratio of arachidonate to linoleate in plasma and liver, but apparently not tumor phosphatidylcholine. The results indicate that the trans-fat is at least equally effective as cis-f&t in terms of mammary tumorigenesis.