Enhancement of Mammary Carcinogenesis with 7, 12 -Dimethylbenz (a) anthracene in Female Rats by High Fat Diets

Abstract

The influences of the semisynthetic diets containing either corn oil or coconut oil at high percentage upon the mammary carcinogenesis with DMBA were investigated in the intact, young adult female Sprague-Dawley rats. Experimental rats were maintained on a control diet, CMF type of the pellet supplied by Oriental Yeast Co., except the period of special feeding. The control diet contained 8 % fat, and the high fat diet was almost isocaloric although it contained 20% fat. In the first experiment, the special feeding of 2 different high fat diets was done either in the age of 35-65 days for initiation stage of tumorigenesis or in the age of 89-149 days for promotion stage of the tumor growth, and the rats were injected intravenously with 3 mg of DMBA at the age of 56 and 59 days. In the second experiment for the initiation stage, the special feeding was done in the age of 45-75 days and DMBA was injected at the age of 66 and 69days. The rats were observed 3 months after the last injection of the carcinogen. The time of appearance of the first palpable tumor was dated from the first injection of DMBA. Mammary cancers, verified by histological examinations, were counted in the gross at necropsy. Total mammary cancers per an animal were weighed on a balance.
Generally, the mammary carcinogenesis could be accerelated more or less by the high fat diets. Especially, the semisynthetic diet containing 20 % corn oil enhanced the development of the mammary cancer by DMBA, and the effect would be exerted mainly at the promotion stage. Coconut oil, presumely providing the animals with a comparably equal energy as that of corn oil, could not exert the same enhancing influence. This phenomenon lends also support to the suggestion that the effect of dietary lipids upon the certain tumorigenesis is not merely a product of an increased caloric intake.
Small pieces of the abdominal mammary fatty pads were resected at the t ime of DMBA administration and of sacrifice, from which lipids were extracted 3 times with a mixture of chloroform and methanol. The lipids extracted were metanolized and analyzed by gasliquid chromatography. The fatty acid composition of some induced mammary tumors by DMBA and of 3 different semisynthetic diets were also determined. The fatty acid compositions of the mammary fatty pads and of the induced tumors were different from each others in the 3 different diet groups, reflecting their fat intakes. DMBA mammary carcinogenesis would be related to the nature as well as the amount of dietary fat of the hosts.