Growth regulation of the rat mandibular condyle and femoral head by transforming growth factor-{beta}1, fibroblast growth factor-2 and insulin-like growth factor-I.

The mandibular condyle is a major growth site and is known to adapt to functional factors. Numerous studies have been performed on the effects of growth factors on the metabolism of primary cartilages, but only a few investigations have examined their action on primary and secondary cartilages. Therefore, the purpose of this study was to compare the effects of insulin-like growth factor-I (IGF-I), transforming growth factor-beta(1) (TGF-beta(1)), and fibroblast growth factor-2 (FGF-2) on the growth of secondary cartilage from the mandibular condyle and primary cartilage from the femoral head of new-born rats. In addition, synergy between these growth factors was investigated. The level of glycosaminoglycan (GAG) and DNA synthesis was analysed after 5 days in culture with the growth factors. The effects of TGF-beta(1) and FGF-2 on growth, tissue organization, and the GAG and collagen content were also evaluated. The stimulation of cell proliferation by the growth factors was higher in the mandibular condyles than in the femoral heads. The content of the matrix components was reduced more by FGF-2 in the mandibular condyles than in the femoral heads. Both TGF-beta(1) and FGF-2 antagonized the stimulatory effects of IGF-I on GAG synthesis in the two types of cartilage. In contrast, the total growth of mandibular condyles was not affected by TGF-beta(1) and FGF-2 while that of femoral heads was strongly reduced. This was mainly due to the inhibition of chondrocyte hypertrophy. These results show that in spite of the extensive effects of growth factors on the metabolism of mandibular condyles, their dimensional growth was not affected.