Polyunsaturated fatty acids as promoters of mammary carcinogenesis induced in Sprague-Dawley rats by 7,12-dimethylbenz[a]anthracene.

The development of mammary tumors was examined in female noninbred Sprague-Dawley rats fed either a low-fat diet or high-fat diets containing different fats and fatty acid esters. Each rat was given 5 mg 7,12-dimethylbenz[a]anthracene by stomach tube 1 week before diets were introduced. Addition of 3% ethyl oleate (an ethyl ester of an unsaturated fatty acid) to a diet high in saturated fat (coconut oil) had no significant effect on tumor development, but the addition of 3% ethyl linoleate (an ethyl ester of a polyunsaturated fatty acid) increased the tumor yield to about twice that in rats fed either the high-saturated fat diet or a low-fat diet. Animals fed the high-saturated fat diet containing 3% ethyl linoleate developed as many tumors as those fed a 20% sunflower seed oil diet, though the sunflower seed oil diet contained about four times as much linoleate. Rats fed a high coconut oil diet containing 3% menhaden fish oil, which contains polyunsaturated fatty acids of the linolenate family (but having little linoleic acid), also developed as many tumors as those fed the 20% sunflower seed oil diet. These differences in mammary tumor yield could not be explained by alterations in the serum levels of prolactin, estrogen, or progesterone. However, the higher tumor yields were associated with increased unsaturation of mammary tissue phospholipids.