ABSTRACT
PURPOSE: This study was performed to examine any histopathological changes occurring in the growth plate when the rats were subjected to be deprived of normal weight bearing using the hindlimb suspension model, and to search for any countermeasures for improving and/or recovering the chondrocyte activities within the growth plate. MATERIALS AND METHODS: Sixty male Sprague-Dawley rats, aged 6 weeks, were divided into 10 groups each: Group I-control to unloading; Group II-unloading 3 weeks only; Group III-unloading+application of heat shock; Group IV-unloading+application of antioxidant; Group V-unloading+application of heat shock and antioxidant; Group VI-control to reloading; Group VII-reloading 1 week only; Group VIII-reloading+application of heat shock; Group IX-reloading+application of antioxidant; Group X-reloading+application of heat shock and antioxidant. The animals were double labeled with 5-Bromo-2'-deoxydiuridin (BrdU) and BrdU immunohistochemistry was performed for the cellular kinetic analysis. Transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) assay was done for the investigation of apoptotic changes in the growth plate, and the positive cells were counted in each zones of the growth plate in both TUNEL and BrdU immunohistochemistry. Heat shock protein (HSP), indian hedgehog (Ihh), and vascular endothelial growth factor (VEGF) were immunolocalized to assess the chondrocytic activities in terms of production of extracellular matrix protein. RESULTS: Non-weight bearing induced a reduction of height of the growth plate, reduced cellular proliferation of chondrocytes, reduced expression of Ihh and VEGF, and altered expression of heat shock protein. When heat shock and/or antioxidant were applied to the unloaded and reloaded rats, only rats in the group of application of both heat shock and antioxidant showed normal cellular activities in terms of cellular proliferation and the production of extracellular matrix protein. CONCLUSION: The present results suggest that application of heat shock and antioxidant would be a countermeasure for the restoration of chondrocytic activities when the normal weight-bearing is deprived of.