HISTOLOGICAL AND HISTOCHEMICAL STUDIES ON THE ARTICULAR CARTILAGE AND GROWTH PLATE OF RATS

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Histological and histochemical studies were made of the femur, patella, and sternum of 20 clinically normal Sprague-Dawley rats at 6 and 12 months of age. Histological changes consisted of loosening of the matrix and degeneration of the chondrocytes of the articular cartilage in the femur and patella. These changes were detected in the femur at 12 months of age and patella at 6 and 12 months of age. In the femur, erosion was also observed at 12 months of age. Furthermore, proliferation of chondrocytes in the radial zone of the femur and marginal chondrophyte in the patella were seen at 12 months of age. In the growth plate, degeneration of the matrix and necrosis were seen in the femur and sternum at 6 and 12 months of age. Closure of the growth plate began in the femur at 12 months of age. Histochemically, glycosaminoglycans (GAGs) were detected in the transitional and radial zones of the articular cartilage of the femur, and these decreased in the transitional zone with increasing age. The changes in the patella were essentially the same as those in the femur. GAGs, especially hyaluronic acid, were increased in the area of proliferated chondrocytes in the femur and marginal chondrophyte of the patella. GAGs were widely distributed in the growth plate of the femur and sternum at 6 months of age. Reduction of GAGs was conspicuous in the femur at 12 months of age.