Conclusion
The second hit phenomenon is probably due to systemic factors rather than to a diminished regenerating potential of injured soft tissues.
Methods
Cold lesion injury was performed in the soleus muscle and in the motor cortex of anesthetized male Wistar rats 0, 1, or 2 times with 7 day intervals between the interventions. Following the last operation, 5-bromo-2'-deoxyuridine was injected i.p. for 6 or 12 days to label dividing cells. Gut epithelium was used as positive control. Immunohistochemistry was performed 1 and 5 weeks after the last injury and the sections were analyzed with confocal microscopy.
Results
In the case of repeated trauma, the percentage of proliferating cells remained the same compared to single hit animals after 1 week (28.0 ± 2.5% and 29.6 ± 3.0%) as well as after 5 weeks (13.9 ± 1.8% and 14.5 ± 2.2%).