Mucopolysaccharides in synovial fluid. Effect of aspirin and indomethacin on hyaluronic acid.

Intra-articular inflammation is associated with a reduction in viscosity of synovial fluid which is due to changes in hyaluronic acid rather than in the protein component of the fluid (Kulonen, 1951; Sundblad, 1953). Hyaluronic acid is a polymer of molecular weight greater than 1 x 106 made up from repeating units of N-acetyl-D-glucosamine and D-glucuronic acid. It is present in concentrations of about 0 1 g. per cent. or less in rheumatoid synovial fluids, compared with 0 3 g. per cent. in normal fluids. Synovial fluid shows anomalous viscosity, i.e. the viscosity decreases with increasing rate of shear, typical of a non-Newtonian fluid. The relative viscosity of a solution of synovial fluid, defined as the viscosity of the solution divided by the viscosity of the solvent, decreases with age (Jebens and Monk-Jones, 1959) and that of rheumatoid synovial fluid is usually lower than normal (Ropes, Robertson, Rossmeisl, Peabody, and Bauer, 1947; Ragan and Meyer, 1949). However, only slight reductions have been found when normal and rheumatoid fluids have been diluted to the same low concentration (0 06 g. per cent.) of hyaluronic acid (Hamerman and Schuster, 1958); this suggests that it is the amount rather than the nature of the hyaluronic acid which determines the relative viscosity. Measurements of intrinsic viscosity, determined by extrapolation of the specific viscosity (i.e. relative viscosity 1) to zero concentration of solute, and anomalous viscosity give a more accurate picture of the state of hyaluronic acid in solution. The lower values of both these parameters for rheumatoid fluids have been attributed to a low mean degree of polymerization of hyaluronic acid in rheumatoid disease (Seppala, 1964; Brimacombe and Webber, 1964). Changes similar to those found in