Biochemical composition of equine carpal articular cartilage is influencedby short-term exercise in a site-specific manner

It was hypothesized that cartilage macro-molecular characteristics are infl uenced by exercise intensity and by location within a joint Objective: To determine the macromolecular characteristics of carpal articu lar cartilage at common and uncommon sites of pathology in horses undergoin g high or low intensity exercise, and to compare this composition between e xercise groups. Design: Twelve horses (19.3 +/- 0.9 years) were assigned to exercise groups . Each group underwent 19 weeks high-intensity treadmill training (N=6) or low-intensity exercise (N=6). Dorsal and palmar test sites were identified on radial, intermediate and third carpal articular surfaces after euthanasi a. Cartilage was collected from each site, freeze-dried and assessed for wa ter content. Hydroxyproline, glycosaminoglycan and DNA analyses were perfor med on cartilage from each test site. Adjacent cartilage underwent histolog ical preparation and assessment for chondrocyte numerical density at each s ite and proteoglycan distribution through the depth of cartilage. Results: Dorsal cartilage had a higher collagen content, DNA content, and c hondrocyte numerical density, but lower glycosaminoglycan content than palm ar cartilage. Cartilage from horses undergoing high-intensity training had a significantly higher glycosaminoglycan content than cartilage from horses undergoing low-intensity exercise, with maximal difference being observed in cartilage from dorsal radial and dorsal intermediate carpal articular su rfaces. Overall no effect of exercise on collagen was observed, but at site s predisposed to clinical lesions cartilage from horses undergoing high-int ensity training contained significantly less collagen than from horses unde rgoing low-intensity exercise. Distribution of proteoglycan was non-uniform in 52% of the sections examined, with superficial loss of toluidine blue s taining primarily at dorsal sites and in the high-intensity exercise group. Conclusions: These results indicate that topographical and exercise related differences exist in carpal cartilage composition, and that the effect of exercise on overall composition and distribution within the cartilage was m aximal at sites predisposed to clinical lesions. These findings could indic ate that the combined effect of exercise and local load variations within a joint may lead to a risk of exceeding the physiologic threshold at high lo ad sites that are predisposed to clinical injury. (C) 2001 OsteoArthritis R esearch Society International.