Subcutaneous implantation of demineralized bone matrix induces the local formation of cartilage and bone. In this study we have investigated the influence of adding various growth factors to the implant. Cartilage formation was monitored by measuring collagen II mRNA levels, and bone formation in the implant was assessed from alkaline phosphatase activity and calcium content. Supplements of the platelet-derived growth factor to implants in older rats increased and production of mRNA for collagen II, alkaline phosphatase activity, and the calcium content of the implant, whereas the other growth factors tested were without effect. The data suggest that under some conditions bone induction is submaximal and can be increased by local supplement of platelet-derived growth factor (PDGF). The present observations may have important therapeutic implications in the treatment of nonunions of fractures and impaired bone formation in the aged.

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