COORDINATED REGULATION OF HYALURONAN AND AGGRECAN CONTENT IN THE ARTICULAR-CARTILAGE OF IMMOBILIZED AND EXERCISED DOGS

Objective. To study the influence of joint loading and immobilization on articular cartilage hyaluronan concentration and histological distr ibution in the knee joints: of young dogs subjected to II weeks' immob ilization by splinting, and 15 weeks' running exercise at a rate of 40 km/day. Methods. The amount of hyaluronan in articular cartilage was determined by a competitive binding assay using a biotinylated hyaluro nan binding complex (HABC) of aggrecan and link protein. Histologic se ctions were stained for the localization of hyaluronan with the HABC p robe. Extracted proteoglycans were characterized by sodium dodecyl sul fate agarose gel electrophoresis. Results. Immobilization significantl y reduced the concentration of hyaluronan in all sites studied (tibial and femoral condyles, patellar surface of femur). The proportion of h yaluronan to total uronic acid (mainly from aggrecan) remained unchang ed because of a concurrent decrease in aggrecan. The ratio of hyaluron an and aggrecan remained constant also in runners. The staining patter n of free hyaluronan in the tissue sections and the electrophoretic mo bility of the extracted proteoglycans were not affected by the differe nt loading regimes. Conclusion. Reduced joint loading due to splint im mobilization significantly decreases both hyaluronan and aggrecan in t he articular cartilage. The remarkably parallel changes in aggrecan an d hyaluronan content suggest that joint loading exerts a coordinated i nfluence on their metabolism.