Exogenous hyaluronidases and degradation of hyaluronic acid in the rabbit eye

The infusion of two enzymes that degrade hyaluronic acid - testicular hyaluronidase and Streptomyces hyaluronidase - was evaluated by quantitative aqueous perfusion of rabbit eyes and by analyses of glycosaminoglycans (GAGs) isolated from the enzyme-treated eyes. The infusion of 1 and 10 units of Streptomyces hyaluronidase (SH) was considerably more effective than the infusion of 10 and 100 units of testicular hyaluronidase (TH) in reducing aqueous outflow resistance. As a result of the infusion of heat-inactivated enzymes, only a moderate decrease of hyaluronic acid in the aqueous outflow pathway was observed. There was no significant 'wash-out' of other GAG material, ie, keratan sulfate, heparan sulfate, and hybrid dermatan sulfate-chondroitin sulfate. The SH enzyme, tested by infusion and isolation of GAGs or by in vitro analyses of the rate and extent of degradation of GAGs, completely removed all hyaluronic acid and did not alter the other GAGs. In contrast, the TH enzyme was only partially effective in degrading susceptible GAGs. The results of these studies indicate that SH is more effective than TH in decreasing aqueous outflow resistance and that hyaluronic acid is an important GAG contributor to aqueous outflow resistance in the normal rabbit eye.