Influence of Dietary Fat on Growth of Mammary Cancer in Rats: Especially Delayed Turnover of Fatty Acid Composition in Tumor Tissue

Abstract

Young adult Sprague-Dawley female rats, given CMF pellet and tap water ad libitum, were injected twice with DMBA around 8 weeks of age. The rats of 4 experimental groups were administered daily a definite amount of 4 different semisynthetic isocaloric diets (8 and 20% coconut oil diets and 8 and 20% corn oil diets), respectively, in the stage between the 12th and 20th week of age, and then they were given again CMF pellet. The control rats, either with DMBA or without the carcinogen, were fed on CMF pellet throughout the experiment. Both the induced mammary cancers and the mammary fatty pads were harvested either 0,2,4,7,10, and 13 weeks after the exchange to CMF pellet in the experimental groups or on the same ages as experimental groups in the controls, and they were investigated by histopathologic examinations, gaschromatographic observations for fatty acid composition, and radioautographic determinations for thymidine uptake. Fatty acid compositions in both tissues of the experimental rats reflected those of the diets ingested, respectively, and the reflection was greater in the higher fat diet groups. On the mammary cancer tissues, polyunsaturated fatty acids, probably related to phospholipids, could be detected more. After the exchange to CMF pellet, the reflection of the former diet, e. g. lauric acid in coconut oil diet group, on the neoplastic tissues remained in more prolonged duration than on the mammary fatty pads. Thymidine uptake into both the mammary fatty pads and mammary cancers increased on the corn oil diet group, especially higher fat diet group. DNA synthesis within the tumor tissues might be accelerated by altered membrane permeability owing to increased polyunsaturated fatty acids. Influence of the high fat diet on promotion of mammary cancer might be concerned mainly with more reflection of dietary fats and slower turnover of fatty acids in the tumor tissues.