Studies on Spreading Factors I. the Importance of Mechanical Factors in Hyaluronidase Action in Skin* by Oscar

I t is generally agreed that there is a close relationship between spreading factors (S. F.) from testis, bacteria, venoms, and other sources with the mucolyric enzyme, hyaluronidase (cf. the review of Duran-Reynals (1) for references). While it is known that hyaluronidase removes a dermal barrier (presumably hyaluronic acid) to the diffusion of fluids in skin certain aspects of hyaluronidase spreading activity are little understood. For example, there is no explanation for the flat upper portion of the sigmoid dosage-response curve of S. F. (2). To state that this result is simply due to saturation of the skin substrate with hyaluronidase, ignores the fact that the entire skin is potentially available for the enzyme and that the amount of substrate is not constant in this system. The fact that above a maximal concentration of hyaluronidase increasing enzyme concentration has so little effect in increasing the area of spread might be attributed to the operation of one of the following mechanisms: (a) Normal skin may contain an active inhibitor of hyaluronidase, which inactivates the enzyme at a rate dependent upon the hyaluronidase concentration. (b) Hyaluronidase may be adsorbed on some constituent of skin, so that it is retained close to the site of injection. This possibility, suggested by Evans and Madinaveitla (3) has not been tested experimentally. (c) Intradermally injected hyaluronidase may be rapidly inactivated as in (a) by a circulating antihyaluronidase which can readily pass through the capillary wall. Normal serum is known to contain antihyaluronidase activity (4-7), although no information is available concerning the rate of diffusion of this factor through the capillary wall. (d) Hyaluronidase may be rapidly absorbed directly into the circulatory system, or indirectly v/a the lymphatics, and thus be eliminated from the skin. (e) The diffusion of hyaluronidase in skin may be controlled by the pressure associated with the injection of fluid, so that the enzyme can diffuse only to an area determined by the volume injected. The above possibilities have been examined in this study.