Effect of fish oil on development of mammary gland and colon tumors induced by methylnitrosourea in target organs of rats

In experiments with adult female rats was studied effect of fish oil on development of mammary gland and colon tumors induced by methylnitrosourea (MNU) using a multi-organ carcinogenesis model. MNU in saline solution administered directly into the target organs: one injection of 1 mg locally in each 12 mammary glands and four intrarectal instillations of 4 mg one time per week. Then rats were given fish oil or sunflower oil (control), 1 ml/rat per day five times a week by gavage for the consecutive 6 months. To the end of experiments when rats were sacrificed in groups with treatment of MNU tumors were detected in 85,7-92,9 %, more half of its were multiple tumors (more often adenocarcinomas) of mammary gland and colon. Sunflower oil did not have significant effect on the carcinogenesis. In rats from fish oil + MNU group compared with the MNU-control group the incidence and multiplicity of mammary tumors were significantly decreased by 1.6 and 3.1 times, correspondingly. Fish oil had less inhibitory effect on the development of colon tumors: decrease of tumor multiplicity (by 1.6 times) was detected only in comparison with MNU + sunflower oil group. These results are interesting for consequence study and use of fish oil as oncoprotector.