EFFECT OF DEPLETION OF INTERSTITIAL HYALURONAN ON HYDRAULIC CONDUCTANCE IN RABBIT KNEE SYNOVIUM

1. The hydraulic resistance of the synovial lining to fluid outflow fr om a joint cavity ((Q) over dot (s)) is important for the retention of intra-articular lubricant. The resistance has been attributed in part to extracellular glycosaminoglycans, including hyaluronan and chondro itin sulphates. Increased permeability in joints infused with testicul ar hyaluronidase, which digests both chondroitin sulphates and hyaluro nan, supports this view. In this study the importance of interstitial hyaluronan per se was assessed using leech and Streptomyces hyaluronid ases, which degrade only hyaluronan. 2. Ringer solution was infused in to the knee joint cavity of anaesthetized rabbits for 30 min, with or without hyaluronidase, after which intra-articular pressure (P-j) was raised and the relation between pressure and outflow determined. 3. Tr eatment with Streptomyces, leech or testicular hyaluronidases increase d the fluid escape rates by similar factors, namely 4- to 6-fold. Afte r Streptomyces hyaluronidase treatment the slope d(Q) over dot (s)/dP( j), which at low pressures represents synovial hydraulic conductance, increased from a control of 0.90 +/- 0.20 mu l min(-1) cmH(2)O(-1) (me an +/- S.E.M., n = 6) to 4.52 +/- 0.70 mu l min(-1) cmH(2)O(-1). The s lope d(Q) over dot (s)/dP(j) increased to a similar level after testic ular hyaluronidase, namely to 4.14 +/- 1.06 mu l min(-1) cmH(2)O(-1) ( control, 0.54 +/- 0.24 mu l min(-1) cmH(2)O(-1)). Streptomyces and lee ch hyaluronidases were as effective as testicular hyaluronidase (no st atistically significant differences) despite differences in substrate specificity. 4. It was shown using histochemical and immunohistochemic al techniques that hyaluronan was removed from the synovium blv leech, Streptomyces and testicular hyaluronidases. The binding of antibodies ,2-B-6 and 3-B-3 showed that the core proteins of the chondroitin sulp hate proteoglycans remained intact after treatment with hyaluronidases , and the binding of 5-D-4 showed that keratan sulphate was unaffected . An azocasein digestion assay confirmed that the hyaluronidase prepar ations had no significant proteolytic activity. 5. The effect of the h yaluronidases was four times greater than predicted from the low conce ntration of interstitial hyaluronan and its resistivity Factors that m ight amplify the effect of hyaluronan depletion include the matrix-org anizing role of hyaluronan, and/or non-uniformity of hyaluronan distri bution. It is concluded that interstitial hyaluronan makes a major con tribution to synovial hydraulic resistance, but the mechanisms are as yet poorly understood.