Evolution of substance P immunofluorescent nerves in callus tissue during fracture healing.

Tibial fractures were experimentally produced in rats. The fractures were allowed to heal spontaneously. Samples of callus tissue were studied by a specific immunohistochemical method for substance P, the peptide which is found in sensory nerves and probably plays a role in nociceptive nerve transmission. The control periosteum contained a rich network of substance P immunofluorescent nerves. The early callus tissue also contained such sensory nerves, the peak frequency of which was at the end of the second week. It is proposed that the substance P-containing nerves play a protective nociceptive role during fracture healing.