The effect of X-irradiation on skeletal muscle regeneration in the adult rat.

Muscle regeneration was induced by transplanting the extensor digitorum longus (EDL) muscle in adult rats to examine the effect of X-irradiation on muscle regeneration. The EDL muscles were removed, irradiated with X-rays to administer 650 R, 2,000 R or 10,000 R, and transplanted into the original animal and location. Muscles from non-irradiated control group and each irradiated group were analyzed morphologically at 4, 7, 14 and 30 days post-transplantation. The regeneration pattern in the non-irradiated and 650-R irradiated muscles was similar. A majority of myofibers underwent degeneration followed by regeneration from the precursor myosatellite cells. The myosatellite cells proliferated, differentiated into myoblasts and then fused to form myotubes and myofibers. Muscles exposed to 2,000 R underwent initial degeneration and myosatellite cell activation, however, considerably fewer myotubes regenerated in these muscles. In muscles exposed to 10,000 R, again myofiber degeneration and myosatellite cell activation was evident, but these cells remained undifferentiated and did not fuse to form myotubes. These results show a dose-dependent inhibition in muscle regeneration due to irradiation.