EFFECT OF COMPREHENSIVE LOADING AND UNLOADING ON THE SYNTHESIS OF TOTAL PROTEIN, PROTEOGLYCAN, AND FIBRONECTIN BY CANINE CARTILAGE EXPLANTS

Full-thickness canine articular cartilage explants were subjected to c ompressive loads equivalent to a uniaxial stress of 0.025-1.2 MPa. A s ingle cycle (18 h) of unconfined compression resulted in inhibition of total protein, proteoglycan, and fibronectin synthesis. The inhibitio n of fibronectin synthesis followed that of total protein synthesis. T he magnitude of inhibition increased nonlinearly with increasing load levels. The signal that depressed synthesis remained effective for sev eral hours after removal of load, but by 24 h proteoglycan synthesis h ad partially recovered and fibronectin and protein synthesis had fully recovered and sometimes exceeded the rate of synthesis in free-swelli ng controls. Forty-eight hours after five cycles of intermittent uncon fined compression with similar loads, proteoglycan content and synthes is did not differ in loaded disks and in disks that were never loaded in vitro. Interestingly, the percentage of water in disks that had nev er been loaded in vitro increased significantly after 10 days in cultu re, relative to the percentage of water in free-swelling disks on the day of harvest. Intermittent compressive loading in the range of 0.5-1 .2 MPa partially prevented this increase. Our results confirmed the pr eviously reported inhibition of biosynthesis with static loading but a lso suggested that exposure to intermittent compressive loading may he lp to maintain the normal ratio of dry to wet weight in the explant.