The evidence is increasing for a close link between the insulin/insulin-like growth factor (IGF) system and colon cancer prevention by physical exercise. To reveal exercise-induced alterations in colon mucosa, gene expression of IGF-1 and related genes and serum IGF-1 were investigated. Twenty male Wistar rats performed a 12 week voluntary exercise program. Nine rats served as the control group. Gene expression of IGF-1, IGF-1 receptor (IGF-1R) and IGF-binding protein 3 (IGF-BP3) were quantified by real-time RT-PCR. Circulating IGF-1 was analyzed exercise volume-dependent. Based on 3 distinguished groups with low (L-EX, <2629 m·night^-1), medium (M-EX, 3003-7458 m·night^-1) and high exercise volume (H-EX, >8314 m·night^-1), we observed lower serum IGF-1 levels (P < 0.05) in all exercise groups as compared to the control group and IGF-1 levels declined proportional to the increase in exercise volume. A significant (p < 0.05) positive correlation was found between IGF-1 concentration and body mass (r = 0.50) and a significant negative correlation exists between body mass and exercise volume (r = -0.50). Significant differences in colonic mRNA levels of IGF-1, IGF-1R and IGF-BP3 could not be observed. Based on our data we propose that the exercise as well as the body mass reduction leads to a decrease in circulating IGF-1 and this might represent a prime link to colon cancer prevention.

• There were significantly lower serum IGF-1 levels in all exercise groups as compared to the control group.

• GF-1 levels declined proportional to the increase in exercise volume.

• A significant positive correlation was found between IGF-1 concentration and body mass and a significant negative correlation was found between body mass and exercise volume.

• Significant differences in colonic mRNA levels of IGF-1, IGF-1R and IGF-BP3 could not be observed.