THE ROLE OF INSULIN-LIKE GROWTH-FACTOR-II IN MAGNETIC-FIELD REGULATION OF BONE-FORMATION

Musculoskeletal tissue is uniquely sensitive to biophysical input, as demonstrated by both mechanical and electrical stimulation experiments . However, the mechanism by which biophysical input couples to cellula r processes is not well understood. The results presented in these stu dies suggest that these stimuli are bioactive due to stimulation of gr owth factor biosynthesis by musculoskeletal target cells. We chose ins ulin-like growth factors (IGFs) as the model growth factor, as the IGF s are capable of stimulating chemotaxis, proliferation, and differenti ation of osteoprogenitor cells. These specific studies addressed wheth er short-term exposure to combined a.c. and d.c. magnetic fields (CMF) would increase production of IGF-II by both osteoblast-like cell cult ures as well as rat fracture callus cultures. In vitro studies on huma n osteoblast-like cell cultures demonstrated statistically significant increases in IGF-II levels and DNA synthesis after only 30 min CMF ex posure. In rat fracture callus explant cultures, IGF-II levels were in creased at least two-fold dependent on the callus differentiation stag e, and these results were comparable with the effect of the osteotropi c agent, parathyroid hormone. In summary, these results suggest that t he mechanism by which CMF, and other biophysical stimuli, regulate mus culoskeletal repair is by modulation of endogenous growth factor (IGF- II) synthesis and secretion.