The differentiated granulation tissue of an interfragmental gap was investigated with help of a distance osteosynthesis model of the rabbit tibia from day 5 to day 25. Antibodies were used against β-actin NOS-I, NOS II, NOS III, COX 2, NF-κB, PKC-2 and collagen I. β-actin proves to be a immunohistochemical marker of osteoneogenesis in the interfragmental gap. Precursor cells (day 5 postoperative), osteoblasts, endothelial cells (day 10 postoperative) and osteocytes (day 15 and day 20 postoperative) express β-actin which can be seen in a diffuse immunoreactivity in the cytoplasm up to legible stress fibers. From isoenzyme NOS only the inducible form NOS II could be demonstrated immunohistochemically. Praeosteoblasts and praeendothelial cells are equal immunoreactive at the 5.th and 10.th postoperative day. Endothelial cells alone express NOS II from the 15th to the 25th postoperative day at the end of the investigation. The proof of NOS II immunoreactivity with representation of β-actin marks a step for differentiation. Only β-actin and in no case NOS-II were recordable as precursor cells are differentiated finally to osteoblasts. In differentiated endothelial cells only NOS-II immunoreactivity could be represented. Proteincinase C-α and the transcription factor NF-κB are visible immunohistochemically at that point as differentiated osteoblasts synthesize collagen type I (10th to 15 th day postoperative).
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