The effect of epidermal growth factor on the fetal rabbit mandibular condyle and isolated condylar fibroblasts

The loud-bearing sur face of il-le mandibular condyle presents a unique arr angement of tissues consisting of an avascular layer composed largely of co llagen bundles. Fibroblasts are interspersed amongst these bundles and are generally agreed to produce the collagen. The mechanisms controlling develo pment of these tissues have not been determined. This study was conducted t o explore the role of epidermal growth factor (EGF), which appears to be im portant ill the development of many oral tissue types as well as in the gro wth and differentiation of the mandibular condyle. Superficial cells of the fibrous zone of the condyle were isolated from fetal rabbit condyles and [ H-3]thymidine incorporation into, DNA measured. The application of EGF prod uced a significant increase in radiolabel incorporation after 2 days compar ed to 4 days in the controls, suggesting that EGF induced cells to enter S- phase more rapidly. Fetal condyles were also cultured on gelfoam surgical s ponges for up to 21 days. Autoradiography of cultured condyles showed that cells of all three zones may potentially replicate, as indicated by incorpo ration of [H-3]thymidine, All three regions displayed greater increases in cell numbers in samples exposed to EGF than in control samples. The measure ment of zone thickness in condyles cultured on gelfoam sponges with or with out EGF showed that this peptide was able to re-establish thickness. bringi ng it in line with the relation observed when the condyles were isolated in itially, particularly of the intermediate zone over a period of 21 days. As very little autoradiographic labelling occurred at this time-point in any of the zones, the increase in thickness must primarily be due to matrix pro duction. It is concluded that EGF is one factor potentially regulating both replication and differentiation in mandibular condyle and its associated c ells. (C) 2000 Elsevier Science Ltd. All rights reserved.