Equine carpal articular cartilage fibronectin distribution associated withtraining, joint location and cartilage deterioration

Processes involved in equine carpal osteochondral injury have not been esta blished, In other species, fibronectin appears important in chondrocyte-mat rix interactions, and levels are increased in osteoarthritis. This investig ation aimed to (a) describe fibronectin immunoreactivity in the middle carp al joint of 2-year-old Thoroughbreds, (b) determine topographical variation s, (c) compare strenuously trained (Group I)or gently exercised horses (Gro up 2) and (d) describe sites with early osteoarthritis. Group 1 (n = 6) und erwent a 19 meek high intensity treadmill training programme. Group 2 (n = 6) underwent 40 min walking until euthanasia. Dorsal and palmar sites on ra dial, intermediate and third carpal articular surfaces were prepared. Immun ohistochemistry was performed using a biotin-streptavidin/peroxidase method . Cross-reactivity of rabbit antihuman fibronectin antiserum with equine fi bronectin was confirmed using Western blotting, Results showed: (a) fibrone ctin was present primarily in pericellular and interterritorial matrix loca tions, (b) dorsal sites had zonal immunoreactivity compared to palmar sites , (c) Group 1 dorsal radial carpal cartilage had increased superficial stai ning compared to Group 2 and (d) fibrillated cartilage showed increased int racellular and local matrical immunoreactivity (superficial zone), These fi ndings suggest topographical and exercise-related variations in fibronectin distribution, and indicate equine fibronectin is localised at sites of car tilage degeneration and released into the matrix by chondrocytes in the loc al area.