Interactive effect of chondroitin sulphate C and hyaluronan on fluid movement across rabbit synovium

The polysaccharide hyaluronan (HA) conserves synovial fluid by keeping outflow low and almost constant over a wide pressure range ('buffering'), but only at concentrations associated with polymer domain overlap. We therefore tested whether polymer interactions can cause buffering, using HA-chondroitin sulphate C (CSQ mixtures. Also, since it has been found that capillary filtration is insensitive to the Starling force interstitial osmotic pressure in frog mesenteries, this was assessed in synovium. Hyaluronan at non-buffering concentrations (0.50-0.75 mg ml(-1)) and/or 25 mg ml(-1) CSC (osmotic pressure 68 cmH(2)O) was infused into knees of anaesthetised rabbits in vivo. Viscometry and chromatography confirmed that HA interacts with CSC. Pressure (P) versus trans-synovial flow ((2,) relations were measured. Q(s) was outwards for HA alone (1.2 +/- 0.9 mul min(-1) at 3 cmH(2)O, mean +/- s.e.m.; n = 6). CSC diffused into synovium and changed 0, to filtration at low P-j (-4.1 mul min(-1), 3 cmH(2)O, n = 5, P < 0.02, t test). Filtration ceased upon circulatory arrest (n = 3). At higher P-j, 0.75 mg ml(-1) HA plus Q(s) buffered 0. to -3 mul min(-1) over a wide range of Pj, with an outflow increase of only 0.04 +/- 0.02 mul min(-1) cmH(2)O(-1) (n = 4). With HA or CSC alone, buffering was absent (slopes 0.57 +/- 0.04 mul min(-1) cmH(2)O(-1)(n = 4) and 0.86 +/- 0.05 mul min(-1) cmH(2)O(-1)(n = 5), respectively). Therefore, polymer interactions can cause outflow buffering in joints. Also, interstitial osmotic pressure promoted filtration in fenestrated synovial capillaries, so the results for frog mesentery capillaries cannot be generalised. The difference is attributed to differences in pore ultrastructure.