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

S. Sabaratnam, P. J. Coleman, E. Badrick, R. M. Mason* and J. R. Levick

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 (CSC) 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 cmH₂O) was infused into knees of anaesthetised rabbits in vivo. Viscometry and chromatography confirmed that HA interacts with CSC. Pressure (P_j) versus trans-synovial flow (˙Q_s) relations were measured. ˙Q_s was outwards for HA alone (1.2 ± 0.9 µl min^-1 at 3 cmH₂O, mean ± S.E.M.; n = 6). CSC diffused into synovium and changed ˙Q_s to filtration at low P_j (-4.1 µl min^-1, 3 cmH₂O, 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 CSC buffered ˙Q_s to ~3 µl min^-1 over a wide range of P_j , with an outflow increase of only 0.04 ± 0.02 µl min^-1 cmH₂O^-1 (n = 4). With HA or CSC alone, buffering was absent (slopes 0.57 ± 0.04 µl min^-1 cmH₂O^-1 (n = 4) and 0.86 ± 0.05 µl min^-1 cmH₂O^-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.

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