EFFECTS OF PHYSICOCHEMICAL FACTORS ON THE GROWTH OF MANDIBULAR CONDYLES IN-VITRO

Cartilage growth and remodeling are known to be influenced by the bioc hemical and mechanical environment of the tissue. Previous investigato rs have shown that chemical factors that are relevant to mechanical lo ading, such as osmotic pressure and pH, induce changes in cartilage me tabolism in vitro. Using a neonatal rat mandibular condyle culture sys tem, the objectives of the work reported here were to determine (1) ho w the growth is influenced by osmotically applied mechanical loads; an d (2) whether changes in intratissue osmotic pressure or pH cause meta bolic changes in the cartilage which are then reflected by altered gro wth behavior. High molecular weight (MW) uncharged macromolecules poly vinylpyrrolidone (PVP) and Ficoll (presumed unable to penetrate the ti ssue matrix) were used to examine the effect of osmotic loading on tis sue growth; concentrations corresponding to osmotic pressures of up to 100 kPa resulted in a dose-dependent depression in growth and matrix accumulation. Raffinose (which can penetrate the matrix but not the ce lls) had no significant effect on growth for osmotic pressures of up t o 87 kPa, suggesting that compression-induced changes in intratissue o smotic pressure are unlikely to provide a signal by which cells sense and respond to mechanical compression. By contrast, changes in medium pH resulted in dose-dependent changes in growth behavior. Specifically , slight alkalinity (acidity) greatly enhanced (diminished) growth and matrix accumulation; the sensitivity to pH suggests that intratissue pH could provide a mechanism for cells to sense local glycosaminoglyca n concentration and mechanical compression. These data are also signif icant in that, while previous investigators have shown that osmotic fo rces and pH affect biosynthetic rates in short-term culture, the prese nt studies indicate that resultant changes in biosynthesis lead to alt ered growth rates.