DISTRIBUTION AND QUANTIFICATION OF PYRIDINIUM CROSS-LINKS OF COLLAGENWITHIN THE DIFFERENT MATURATIONAL ZONES OF THE CHICK GROWTH-PLATE

In order to assess alterations in the collagen network during endochon dral ossification the pyridinium cross-links of collagen were quantifi ed in sequential transverse sections through the chick growth plate. T his was accomplished using both morphological (alkaline phosphatase (A LP) histochemistry and collagen type X immunostaining) and analytical (HPLC) analyses. In articular cartilage, pyridinoline concentrations w ere maximal in the deep mature zones. In contrast, the proliferating c hondrocyte zone of the growth plate had approximately a 10-fold greate r pyridinoline cross-link concentration than the mature hypertrophic z one. Deoxypyridinoline was first found in the prehypertrophic zone of the growth plate cartilage that reacted positively for ALP activity bu t before collagen type X was detected. However, deoxpyridinoline conce ntrations were highest in the most differentiated regions of the growt h plate where it was the principal pyridinium cross-link. In tibial dy schondroplasia, where chondrocyte differentiation is arrested in the p rehypertrophic zone, higher concentrations of both cross-links were fo und with increasing distance down the lesion. We conclude that the dec rease in pyridinoline cross-link concentration down the growth plate m ay be an essential adaptation (via increased collagenase activity and collagen turnover) of the matrix for vascular invasion and osteoclasti c resorption to occur.