Molecular analysis of defect healing in rat diaphyseal bone

Spatial expression of messenger ribonucleic acid (mRNA) for osteoblastic ma rker in drill hole defect healing of adult male rats was analyzed by in sit u hybridization. The defect was filled with hematoma 3 days after surgery, expressing Type I collagen mRNA. Hematoma was replaced with fibrous tissue on day 7, and then with new trabecular bone on day 10, originated from the intra-medullary space. respectively. mRNA for Type I collagen, parathyroid hormone 1 receptor (PTH1R), and alkaline phosphatase (ALP) were expressed i n the same cell population of fibrous tissue adjacent to newly-formed trabe cular bone, and in osteoblasts lining the newly-formed trabecular bone. Hem atopoietic marrow with osteoclasts subsequently invaded the region. also fr om the intra-medullary space, replacing all the new trabecular bone by day 21, except for a thin sub-periosteal layer. mRNA for Type I collagen, PTH1R and ALP was expressed on the periosteal surface of thin layer. Although ca rtilage formation was not histologically visible, mRNA for Type II collagen was weakly detected in the majority of osteoblasts lining the newly-formed trabecular bone.