Regeneration of dystrophic muscle following multiple injections of bupivacaine.

Regenerated myofibers formed subsequent to orthotopic transplantation of young, dystrophic mouse muscle fail to display the extensive histopathological changes characteristics of murine dystrophy. In order to determine whether this modification of the phenotypic expression of murine dystrophy is unique to the transplantation system or whether it can be found when other extreme trauma induces dystrophic muscle to regenerate, the extensor digitorum longus muscles of 4-6-week-old normal (129 ReJ +/+) and dystrophic (129 ReJ dy/dy) mice were given two series of injections of the myotoxin bupivacaine, spaced 12 hours apart. These injections resulted in necrosis of approximately 90% of the original myofibers. At 100 days after injection, the regenerated normal muscle appeared "healthy," whereas the regenerated dystrophic muscle displayed histopathological changes. It is suggested that the differences in the time course of innervation of the myotubes in the transplantation system as compared with that in the bupivacaine system may be a factor in determining whether regenerated dystrophic myofibers express a dystrophic morphology.