CORRELATION OF MORPHOLOGIC AND BIOCHEMICAL-CHANGES IN THE NATURAL-HISTORY OF SPONTANEOUS OSTEOARTHROSIS IN GUINEA-PIGS

Objective. To study how the concentrations of proteoglycans (PGs) and collagen change in various parts of tibial articular cartilage during aging, and to evaluate the development of spontaneous osteoarthrosis ( OA) in guinea pigs. Methods. PGs were extracted from guinea pig cartil age samples using 4M guanidine hydrochloride, and the amount of hydrox yproline was determined in the extraction remainder, The molecular siz e and aggregation of PGs were analyzed by electrophoresis, and the gly cosaminoglycan composition was assessed by highperformance liquid chro matography. Results. The PG concentration was proportional to the load distribution, However, when OA became histologically manifest, the PG concentration decreased by 50% (from a mean of 44 mu g to 22 mu g per mg fresh tissue) and the collagen level decreased by 40% (from a mean of 17 mu g to 10 mu g per mg fresh tissue), while the proportion of w ater increased by 13% (from a mean of 710 mg to 800 mg per mg fresh ti ssue). Conclusion. Unmineralized cartilage can, within physiologic loa d limits, respond to increased mechanical demands by increasing the PG and collagen concentrations, Beyond a certain limit, however, the car tilage can no longer compensate for further increases in stress, which results in cartilage degeneration and losses of matrix constituents. These losses seemed to appear earlier in the disease process than has been described in previous animal models of Secondary OA.