title: Ovariectomy alters the structural and biomechanical properties of ovine femoro-tibial articular cartilage and increases cartilage iNOS.
abstract: OBJECTIVE
  To examine the effect of oestrogen depletion produced by surgical ovariectomy on the structural and biomechanical properties of ovine femoro-tibial articular cartilage (AC), and the production of inducible nitric oxide synthase (iNOS) and nitrotyrosine by these tissues.
  
  
  METHODS
  Six aged ewes were surgically ovariectomised (OVX), while six were used as unoperated controls. Dynamic biomechanical indentation testing of tibial plateau AC was performed at 26 weeks post-op. Histological sections of medial tibial plateau and lateral tibial plateau (LTP), medial and lateral femoral condyles (MFC, LFC) and patellar AC were examined for histopathology, toluidine blue staining intensity, and patterns of collagen birefringence intensity. Immunoreactivity for iNOS and nitrotyrosine was assessed in full-thickness biopsy plugs of LFC and patellar AC, and patellar AC explants were cultured to determine in vitro NO release.
  
  
  RESULTS
  Phase lag was reduced overall in LTP-AC of OVX sheep (10.9+/-2.2 degrees vs 12.1+/-2.3 degrees ; P<0.0001). Cartilage thickness was reduced in the LTP of OVX sheep (P=0.0002), in association with localised changes in dynamic shear modulus. Toluidine blue staining intensity was reduced in the patella, LFC, and MFC. Histological examination revealed greater histopathology scores in the MFC of OVX animals, and altered collagen birefringence intensity plots in the LTP. Immunostaining for iNOS was increased in patella AC (P=0.008), whilst nitrotyrosine immunoreactivity was increased in patella (P=0.03) and LFC (P<0.0001) AC. NO release by patellar AC explants was also elevated.
  
  
  CONCLUSIONS
  Oestrogen depletion induced by OVX caused regional thinning of femoro-tibial cartilage, with biomechanical and histological changes suggestive of a disturbance in the content and/or structural organisation of the proteoglycan and collagen macromolecular assembly. The observed up-regulation of cartilage iNOS suggests a possible mechanism for these matrix changes.
authors.affiliation: School of Veterinary and Biomedical Sciences, Murdoch University, WA, Australia. mcake@murdoch.edu.au
authors.forename: M A
authors.initials: MA
authors.lastname: Cake
authors.forename: R C
authors.initials: RC
authors.lastname: Appleyard
authors.forename: R A
authors.initials: RA
authors.lastname: Read
authors.forename: M M
authors.initials: MM
authors.lastname: Smith
authors.forename: G A C
authors.initials: GA
authors.lastname: Murrell
authors.forename: P
authors.initials: P
authors.lastname: Ghosh
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000201:enzymology / Q000473:pathology* / Q000503:physiopathology; D004967:Estrogens / Q000172:deficiency*; D005260:Female; D006614:Hindlimb; D007150:Immunohistochemistry / Q000379:methods; D023421:Models, Animal; D009569:Nitric Oxide / Q000032:analysis; D052247:Nitric Oxide Synthase Type II / Q000032:analysis / Q000378:metabolism*; D010052:Ovariectomy; D017698:Postmenopause; D012756:Sheep; D046509:Tissue Culture Techniques
chemical_list: D004967:Estrogens; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II