ULTRASTRUCTURAL STUDIES OF THE EPIPHYSEAL PLATE OF CHICKS FED A VITAMIN-D-DEFICIENT AND LOW-CALCIUM DIET

The epiphyseal plates of rachitic chicks fed a vitamin D-deficient and low-calcium diet were examined ultrastructurally at 4, 7, 14, 18 and 21 days old. On and after 14 days, changes were observed. Chondrocytes in resting, proliferating and maturing zones commonly showed a reduct ion in cell organelles, suggestive of a decrease in synthetic activity of matrix components. In addition, the resting zone cells had numerou s intracytoplasmic microfilaments. Mitotic figures were present but no t increased in number in the proliferating zone. Autolysosome-like den se bodies in the chondrocytes and clusters of degenerative and necroti c chondrocytes were observed in the proliferating and maturing zones. In the calcifying zone of the rachitic epiphyseal plate, initial calci fication was observed characterized by the deposition of apatite cryst als in matrix vesicles and the formation of spherical crystal clusters . The crystal clusters were separated from each other by collagen fibr ils on which only small amounts of apatite crystals had been deposited . In this zone, hypertrophic chondrocytes responsible for the initial calcification were seen, but not the stellate chondrocytes responsible for the progression of matrix calcification after its initiation. The se findings suggest that accumulation of the proliferating and maturin g zone cells as a characteristic lesion of the epiphyseal plate in rac hitic chicks is caused by a disturbance of cell maturation. Such distu rbance in the calcifying zone may explain the progression of the defec t in matrix calcification. (C) 1995 Academic Press Limited