title: Joint immobilization reduces synovial fluid hyaluronan concentration and is accompanied by changes in the synovial intimal cell populations.
abstract: OBJECTIVE
  Synovial fluid (SF) of normal joints contains high hyaluronan (HA) concentrations. However, the mechanism by which these are controlled and how they are influenced by articulation and loading are not established. In this study, we have examined whether immobilization influences SF HA concentration and whether this is associated with alterations in the synovial lining.
  
  
  METHODS
  Hock joints of five adult sheep were immobilized by external fixation. Twelve weeks later, SF and synovium samples were collected. The HA concentration in SF was assayed using an ELISA-based method. Non-specific esterase (NSE) and uridine diphosphoglucose dehydrogenase (UDPGD) activities were assessed in cryostat sections of snap-chilled synovial samples using cytochemical techniques, and UDPGD activity per cell was measured in synovial lining cells by scanning and integrating microdensitometry.
  
  
  RESULTS
  We found that the SF HA concentration was decreased from 1.65+/-0.25 mg/ml in control joints to 0.68+/-0.16 mg/ml in immobilized joints. Synovial intimal cell UDPGD activity decreased from 18.0+/-2.7 U/cell in control joints to 12.2+/-1.5 after immobilization. There was also a decrease in UDPGD-positive intimal cell numbers. Intimal surfaces in controls contained numerous NSE-positive cells, which were rarely observed in intima from immobilized joints.
  
  
  CONCLUSIONS
  These results suggest that immobilization decreases SF HA levels and that this is associated with reduced intimal cell UDPGD activity (essential for HA formation). Immobilization also decreased the prevalence of (NSE-positive) intimal macrophages. These findings suggest that mechanosensitive homeostatic mechanisms exist within the synovial intima.
authors.affiliation: Department of Veterinary Basic Sciences, The Royal Veterinary College, London NW1 0TU, UK.
authors.forename: A A
authors.initials: AA
authors.lastname: Pitsillides
authors.forename: T M
authors.initials: TM
authors.lastname: Skerry
authors.forename: J C
authors.initials: JC
authors.lastname: Edwards
mesh_terms: D000818:Animals; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D002452:Cell Count; D005260:Female; D006820:Hyaluronic Acid / Q000378:metabolism*; D007103:Immobilization; D007596:Joints / Q000378:metabolism*; D012756:Sheep; D013582:Synovial Fluid / Q000201:enzymology / Q000378:metabolism*; D013583:Synovial Membrane / Q000166:cytology / Q000378:metabolism; D014533:Uridine Diphosphate Glucose Dehydrogenase / Q000378:metabolism
chemical_list: D006820:Hyaluronic Acid; D014533:Uridine Diphosphate Glucose Dehydrogenase; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase