Distribution of biologically labelled radioactive hyaluronic acid injected into joints.

Hyaluronic acid is synthesized in the tissues where it is found, a fact which has been amply demonstrated by culture of the appropriate cells in vitro (Vaubel, 1933; Kling, Levine, and Wise, 1955; Grossfeld, Meyer, Godman, and Linker, 1957). The synthetic sequences have also been intensively studied. However, knowledge of the extracellular movement of hyaluronic acid is fragmentary by comparison, although the distribution of tissue hyaluronidases indicates potential sites of breakdown (Bollet, Bonner, and Nance, 1963; Vaes and Jacques, 1965). The widespread distribution of hyaluronic acid virtually requires a radioactive marker to trace its movements. The choice of isotope is limited by the need to incorporate it by covalent bonding, which means at the present time the use of '4Cor 3Hlabelled glucose or glucosamine as a substrate in the initial synthesis of the hyaluronic acid. The low intensity of radiation from these isotopes precludes the use of external counters for tracing, but on the other hand lessens the risk of degradation of the polymer by autoirradiation during a long preparation and storage. After the choice of substrate, there are two possible courses. The substrate can be administered to provide an estimate of the subsequent turnover of the glycosaminoglycans and their intermediates extracted at intervals thereafter (See, for example, Schiller, Slover, and Dorfman, 1962; Hardingham and Phelps, 1968). This is complicated by the potential incorporation of the substrate in other macromolecules. Alternatively, mammalian cell cultures can be used to synthesize hyaluronic acid from isotopic substrates (Yielding, Tomkins, and Bunim, 1957) and the largest polymers selected and purified by gel chromatography (Baxter, Fraser, and Harris, 1973) before study in vivo. This paper describes development of the latter approach to study the fate of hyaluronic acid within synovial joints. Methods