Exercise can prevent bone loss and increase bone density. Growth factors such as insulin-like growth factor-I (IGF-I) and transforming growth factor P (TGFB) are thought to be involved in the local response to mechanical loading, resulting in bone remodelling. We tested the effect of additional weight bearing during exercise on the systemic response of IGF-I and local bone response of IGF-I and TGFP.Thirty-four female Wistar rats (aged 3 months, weight 226.9 4~ 20.2 g) were randomly divided in four groups: group 1 baseline controls; group 2 sedentary controls; group 3 ran 15 min a day on a motor-driven exercise belt: group 4 ran 15 min a day with a backpack containing 40 g. The animals ran 5 days a week, for 6 weeks, with an average velocity of 16.6 i 4.4 mlmin, and a slope of 5" 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-I and I G F binding protein 3 (IGFBP3) levels in serum and the IGF-I levels in liver were similar in all groups. In the tibia no significant differences were observed in IGF-I, IGFBP3 and TGFP concentration. In the 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 that ran with additional weight than in those without ( P = 0.009). The TGFP 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 TGFP in bone appeared to be modulated by running exercise. 0

Sesamoid bone cartilage from the metacarpophalangeal joints of 5-year-old cows was cultured intact on its bone support. The incorporation of sulfate increased similarly in experimental cartilage that was subjected to cyclic loading (0.2 MPa, 0.2 Hz) for a week and in control cartilage that was cultured without loading. The synthesis of a population of small macromolecules decreased in the cultured controls, but was maintained at a constant level in the experimental samples. This population was isolated through Sepharose CL-2B chromatography. Subsequent application to Sepharose CL-4B yielded two distinct peaks. One contained protein-free chondroitin sulfate, keratan sulfate, and possibly some dermatan sulfate glycosaminoglycans. The other, more prominent, peak consisted of dermatan sulfate proteoglycans. This peak material was pooled, and applied to a 4-15% SDS-gel. The material was separated into two major bands, which represented biglycan and decorin. They decreased to less than half their day-0 value, in the cultured control. In the loaded cartilage, biglycan synthesis remained constant while decorin synthesis increased. These findings suggest that biglycan and decorin are involved in the adaptation of articular cartilage to variations in loading regime.

The effect of long distance running exercise (40 km/day for 15 weeks, five days a week) on the decorin content of articular cartilage from the knee joint was studied in female beagle dogs. Samples from load bearing sites on the lateral plateau of the tibia (TL), and pooled material from two minimum load bearing sites on the posterior section of lateral (FLP) and medial (FMP) femoral condyles were analyzed. The running exercise protocol did not lead to significant changes in the overall glycosaminoglycan content of the cartilage. However, the amount of decorin significantly increased in the TL samples, and also in the FMP pool. These results support earlier in vitro observations that decorin synthesis is stimulated by loading, independent of the synthesis of aggrecan.

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