Exercise and tumor development in a mouse predisposed to multiple intestinal adenomas

Epidemiological evidence suggests that physical activity may be protective against the development of colon cancer. Potential mechanisms remain largely unexplored due to the paucity of appropriate experimental models. The purpose of this study was to examine the effect of exercise training on polyp development in an induced mutant mouse strain predisposed to multiple intestinal neoplasia (Min mouse). Three-week-old male and female heterozygotes were randomly assigned to control (CON; 10 males, 6 females) or exercise (EX; 11 males, 11 females) groups. In the first week, EX mice were acclimated to treadmill running at 10-18 m x min(-1) for 15-60 min x d(-1). From 4-10 wk of age, mice ran at 18-21 m x min(-1) for 60 min. CON mice sat in Plexiglas lanes suspended above the treadmill for the same time periods. At 10 wk of age, the mice were sacrificed and the intestines removed, opened, and counted for polyps. Skeletal muscle oxidative capacity increased with training as shown by a 64% increase in citrate synthase activity in the gastrocnemius/soleus muscle of EX compared with CON (P = 0.009). There were no significant effects of exercise in the males and females combined on small intestine, colon, or total intestinal polyps (P > 0.05). When analyzed separately, however, there were fewer colon and total polyps in the EX than in the CON males, although the difference was not statistically significant (P = 0.06). These results suggest that seven weeks of exercise training do not affect the development of intestinal polyps in the Min mouse. Further studies are required to determine if a true sex difference exists or if variations on the current training protocol may affect tumor outcomes.