COUPLING BETWEEN MINERALIZATION CHANGES IN BILATERAL RAT TIBIAL CORALLINE-IMPLANTS

Unstable fractures are known to lead temporarily to bone mineral loss in remote skeletal sites. The present study examines to what extent th e healing of bone defects affects the mineralization of remote bone de fects. Bilateral tibial defects were created in 20 female rats and fil led with coralline implants (Interpore-200). Mineral content (MC) of t he defects was followed nonivasively, 5 times during 57 days, using du al X-ray absorptiometry. Different mineralization rates were experimen tally obtained at the right tibial defects by impregnating the implant s with different estradiol doses. We found that the mineralization rat es in opposing defects were reciprocally coupled. Increased rates of d efect mineralization induced by an adjacent fracture and local estradi ol-effect, were accompanied by a decreased mineralization at the contr alateral defect, and vice versa. The hypothesis that coupling between remote bone defects was mediated by the circulation was tested by exam ining the ability of the rats sera to stimulate osteogenic differentia tion in cultured stromal cells. Sera of rats with low defect mineraliz ation (without fractures) significantly increased osteogenic different iation as indicated by increased specific phosphtase (ALP) activity. C onversely sera of rats with high defect mineralization (with fractures ) failed to increase ALP activity. Sera fractionation showed that diff erences in ALP induction may be attributed to macromolecules which are yet unidentified. These results may suggest that remote bone defects are utilizing systemic mineralization factors, in a competitive manner .