Ultrastructural studies on bone lesions of rachitic chicks

The most characteristic lesions of avian rickets are thickening of the epiphyseal plate, defective calcification of the cartilage matrix, and proliferation of osteoclasts and osteoblasts with an appearance of undifferentiated cells in the metaphysis. However, little attention has been paid to ultrastructure and functional activities of individual cells in the rachitic lesions. Therefore, the pathogenesis of rachitic lesions is still an ill-defined subject. In the present study, the sequential stages of chondrocytic maturation in the epiphyseal plate of normal chicks were examined ultrastructurally with reference to the role of chondrocytes at each stage. Subsequently, the epiphyseal plate, metaphysis and parathyroid gland of rachitic chicks were investigated ultrastructurally and histochemically. In the epiphyseal plate of normal chicks, the resting zone cells manifested an evidence for active protein synthesis, and the proliferating zone cells had the characteristics of duplicate cells showed by the presence of mitotic activity.