Influence of exercise-training on insulin-like growth factor I and II in rats

There are conflicting reports that exercise increases or does not change circulating insulin like growth factors (IGFs) and insulin like growth factor binding proteins (IGFBPs) in humans. In this study, we examined whether endurance exercise training could alter the IGF levels and IGFBP patterns in serum as well as tissues in rats. Sixteen rats were divided into two groups; control and exercised. Rats in the exercised group were exercise-trained 6 days per week on a treadmill (60min./day, 10° incline, 25m/min) for eight weeks. Food intake was not different between the two groups, however, weight gain and feed efficiency were significantly lower in the exercised group than in the control group. Total IGF-I and IGF-II levels in blood and kidney were not different between the two groups, while free IGF-I levels in blood were significantly higher in the exercised group than in the control group. IGF-I and IGF-II levels in liver were significantly higher in the exercised group than in the control group. These results suggest that exercise-training for 8 weeks alters IGF-I and II levels in liver, but not in serum, may alter the bioavailability of IGF-I, and may involve regulator other than IGFBPs.