Modulation of proteoglycan composition in cultured anatomically intact joint cartilage by cyclic loads of various magnitudes.

The anatomically intact articular cartilage (area approximately 2.5 cm2) of 6-month-old bovine sesamoid bones was cyclically (0.3 Hz) loaded with 0, 5, 25 and 50 kg in vitro for 7 days. The amount and composition of the proteoglycans that were synthesized during the last 17 hours of incubation under each regime were studied. Loads of all magnitudes produced a 45% overall increase in synthesis, which included a disproportionate increase in the synthesis of small proteoglycans. Loading with either 25 or 50 kg induced the synthesis of much larger glycosaminoglycan side-chains and a species of small proteoglycan rich in keratan sulfate. Under these greater loads, synthesis in the deep layer of the cartilage was reduced and there was focal damage to the cartilage surface.