BED REST DECREASES MECHANICALLY INDUCED MYOFIBER WOUNDING AND CONSEQUENT WOUND-MEDIATED FGF RELEASE

Using a terrestrial model of spaceflight (i.e., bed rest), we investig ated the amount of myofiber wounding and fibroblast growth factor (FGF ) release that occurs during unloading. Myofiber wounding was determin ed by serum levels of the creatine kinase MM (CKMM) isoform before and after bed rest. Serum levels of both acidic FGF (aFGF) and basic FGF were also determined. A second group of subjects was treated in an ide ntical fashion except that they underwent a resistive exercise program during bed rest. Bed rest alone caused significant (P < 0.05; n. = 7) reductions in post-bed-rest serum levels of both CKMM and aFGF, which were paralleled by a significant (P < 0.05; n = 7) decrease in myofib er size. In contrast, bed rest plus resistive exercise resulted in sig nificant (P < 0.05; n = 7) increases in post-bed-rest serum levels of both CKMM and aFGF, which were paralleled by inhibition of the atrophi c response. These results suggest that mechanically induced, myofiber wound-mediated FGF release may play an important role in the etiology of unloading-induced skeletal muscle atrophy.