Interaction between hyaluronic acid and serum dispersed in collagen gels.

A high degree of viscosity is the most striking physical attribute of normal synovial fluid. Although its direct relationship to the lubrication of joints remains uncertain, this viscosity still reflects physiologically important properties of hyaluronic acid. The anomalous viscosity which is a particular feature of hyaluronic acid in synovial fluid depends not only on the concentration and polymerization of hyaluronic acid (Ogston and Stanier, 1950, 1953), but also on its association with protein. Certain proteins are bound preferentially to hyaluronic acid in abnormal human synovial fluid (Sandson, Hamerman, and Schwick, 1965) and in normal bovine synovial fluid (Curtain, 1955). In the latter case, careful removal of the associated protein greatly reduces the anomalous viscosity without altering other molecular parameters of the hyaluronic acid (Silpananta, Dunstone, and Ogston, 1968, 1969). Far fewer observations have been made concerning the effects of the relatively larger amounts of proteins in the parent synovial fluid, which cover a slightly modified and much less selective range of the serum proteins. The following observations, made for a somewhat different purpose, may have some bearing on this matter. Some gross differences in mucin complexes from hyaluronic acid and fresh or heatinactivated serum proteins with acetic acid (Fraser and Harris, 1971) led us to examine reactions between hyaluronic acid and high concentrations of serum in less drastic conditions. We adopted the ingenious connective tissue model devised by Fessler (1960), who found that incorporation of synovial fluid in collagen gels greatly increased their resistance to compression by centrifugal force. Disalvo and Schubert (1966) had confirmed this finding and further shown that cartilage proteinpolysaccharide exerts an even greater effect on collagen gels than hyaluronic acid. The present study shows that inclusion of extra serum in such a system magnifies the effect of synovial fluid on the compressibility of collagen gels, whereas similar amounts of serum without synovial fluid have virtually no effect. Materials and methods