Effects of physicochemical factors on the growth of mandibular condyles in vitro

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Abstract
Cartilage growth and remodeling are known to be influenced by the biochemical and mechanical environment of the tissue. Previous investigators have shown that chemical factors that are relevant to mechanical loading, such as osmotic pressure and pH, induce changes in cartilage metabolism in vitro. Using a neonatal rat mandibular condyle culture system, the objectives of the work reported here were to determine (1) how the growth is influenced by osmotically applied mechanical loads; and (2) whether changes in intratissue osmotic pressure or pH cause metabolic changes in the cartilage which are then reflected by altered growth behavior. High molecular weight (MW) uncharged macromolecules polyvinylpyrrolidone (PVP) and Ficoll (presumed unable to penetrate the tissue matrix) were used to examine the effect of osmotic loading on tissue 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 cells) had no significant effect on growth for osmotic pressures of up to 87 kPa, suggesting that compression-induced changes in intratissue osmotic 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 glycosaminoglycan concentration and mechanical compression. These data are also significant in that, while previous investigators have shown that osmotic forces and pH affect biosynthetic rates in short-term culture, the present studies indicate that resultant changes in biosynthesis lead to altered growth rates.