Effects of loading on the synthesis of proteoglycans in different layers of anatomically intact articular cartilage in vitro.

The anatomically intact articular cartilage (approximately equal to 2.5 cm2) of whole bovine sesamoid bones was cultured on its bone support. A load of 5 kg was applied intermittently at 0.3 Hz by a specially designed loading apparatus for 7 days. [35S]-sulfate was added during the last 17 h of the experiment. Loading induced a 40% increase in [35S]-sulfate incorporation into aggrecans and an almost 3-fold increase in the synthesis of small proteoglycans. The loading effects occurred mainly in the upper half of the articular cartilage. Samples left unloaded for 7 days and then loaded for 7 days likewise showed an increase in [35S]-sulfate incorporation compared with unloaded controls.