The effect of exercise on systemic and bone concentrations of growth factors in rats

Exercise can prevent bone loss and increase bone density. Growth factors su ch as insulin-like growth factor-I (IGF-I) and transforming growth factor b eta (TGF beta) are thought to be involved in the local response to mechanic al loading, resulting in bone remodelling. We tested the effect of addition al weight bearing during exercise on the systemic response of IGF-I and loc al bone response of IGF-I and TGF beta. Thirty-four female Wistar rats (aged 3 months, weight 226.9 +/- 20.2 g) wer e randomly divided in four groups: group I baseline controls: group 2 seden tary controls, group 3 ran 15 min a day on a motor-driven exercise belts gr oup 4 ran 15 min a day with a backpack containing 40 g. The animals ran 5 d ays a week. for 6 weeks, with an average velocity of 16.6 +/- 4.4 m/min, an d a slope of 5 degrees uphill. The serum growth hormone (GH) concentration was significantly higher in the running rats (group 3. P = 0.009) than in the sedentary controls (group 2) . The IGF-l and IGF binding protein 3 (IGFBP3) levels in serum and the IGF- I levels in liver were similar in all groups. In the tibia no significant d ifferences were observed in IGF-1, IGFBP3 and TGF beta concentration. In th e humerus, the IGF-I concentration was lower in the running rats (group 3) than in the sedentary controls (P = 0.04), but it was higher in the rats th at ran with additional weight than in those without (P = 0.009). The TGF be ta concentration in the humerus was lower in both group 3 (P = 0.001) and 4 (P = 0.03) than in the sedentary controls. The effects in bone caused by mechanical stimulation cannot be explained by changes in serum IGF-I and IGF-I produced in the liver, The concentrations of IGF-I and TGF beta in bone appeared to be modulated by running exercise . (C) 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.