Effect of dietary menhaden oil on tumor cell loss and the accumulation of mass of a transplantable mammary adenocarcinoma in BALB/c mice.

A reduction in the size of transplantable mammary adenocarcinoma IX was achieved when female BALB/c mice were fed isocaloric 10% fat diets containing either hydrogenated cottonseed oil (HCTO) or menhaden oil (MO) as opposed to those mice fed corn oil (CO). Indeed, CO increased the size of the neoplasms when fed alone at 5 or 1% of the diet, although such diets contained less fat calories than did the 10% fat diets containing the other two oils. At the 10% level of dietary fat, enhanced accumulation of tumor mass was observed even when 7.5, 5.0, and 2.5% CO was administered in combination with either HCTO or MO. Although this effect of CO could not be inhibited when nine times as much HCTO was added to the diet, such growth enhancement was abolished when the diet contained nine times as much MO. Hence these experiments emphasized the importance of the type rather than the amount of dietary fat. Whereas MO contained polyunsaturated fatty acids (PUFA's) [approximately 1% as linoleic acid, approximately 16% as 5,8,11,14,17-eicosapentaenoic acid (EPA), approximately 11% as 4,7,10,13,16,19-docosahexaenoic acid (DHA)], HCTO contained none and CO had about 60% of its constituent fatty acids in the form of linoleic acid. The rate of tumor cell loss, determined by the [125I]5-iodo-2'-deoxyuridine method, in the 10% MO-fed or the 10% HCTO-fed mice (54 or 45%, respectively) was more than twice that observed for tumors from the 10% CO-fed mice (22%). These observations were discussed in terms of the influence of the dietary PUFA linoleic acid [C 18:2 (No. of carbons:No. of double bonds), n-6], the PUFA EPA (C 20:5, n-3), and the PUFA DHA (C 22:6, n-3) on the size of mammary tumors and on the involvement of prostaglandins in this process.