Hyaluronidase: correlation between biological assay and other methods of assay.

Different workers have at various times sought to correlate the in vivo and in vitro activities of hyaluronidase preparations. Chain & Duthie (1940), drawing attention to the association between diffusion in the tissues and the mucolytic activity of testicular extracts, pointed out that the viscosityreducing and diffusing activities of various enzyme preparations were in good agreement. McClean (1943) compared enzymes from different sources by their diffusing activity with Humphrey's (1943) technique, by their viscosity-reducing activity at pH 7*0 and by the mucin-clot prevention test; he found that the results of the viscosimetric assay could be very closely correlated to those of the skindiffusing activity. Madinaveitia, Todd, Bacharach & Chance (1940), on the other hand, were unable to correlate satisfactorily the viscosity-reducing activity of hyaluronidase preparation with their skin-diffusing activity and stated that diffusing factors ought not to be assayed in terms of their activity in the physicochemical test. In his review on the biological role of hyaluronic acid and hyaluronidase, Meyer (1947) pointed out that the spreading reaction could not be considered as an accurate assay of hyaluronidase and that the correlation between spreading reaction and physicochemical methods of hyaluronidase assay was poor. In certain instances the comparison was vitiated by the use of different conditions of pH and salt concentration in the different tests, but. even when this was avoided the error ofthe biological assays was too great to permit any conclusion that in vitro tests are a true measure of in vivo activity. The question is of some importance because of the need to standardize hyaluronidase in view of its increasing use in clinical medicine. Having devised a biological method of hyaluronidase assay which gives reproducible results (Jaques, 1953) we undertook to assay seven different enzyme preparations by the more convenient viscosimetric and turbidimetric methods and to correlate the results with those of the bioassay. All tests were performed under approximately physiological conditions of pH and salt concentration in order to imitate more closely the conditions ofthe skin test (McClean, 1941, 1943).