Osteogenic activity of growth cartilage examined by implanting decalcified or devitalized ribs and costal cartilage zone, and living growth cartilage cells.

The formation of cartilage prior to bone in an endochondral bone formation process suggests that some osteogenic factors exist in the cartilage. This osteogenic activity of cartilage or cartilage cells was examined by implanting ribs and costal cartilage zone into a subcutaneous pocket of abdominal wall, or the growth cartilage (GC) cells into a peritoneal cavity. Rib segments of young (four-week-old) rabbits and rats were decalcified (DCed) in 0.6 N HCl for 24 h at 4 degrees C, or devitalized (DVed) by freezing/thawing and submerged in water for 48 h at 4 degrees C. These specimens were implanted into the subcutaneous pocket of abdominal wall of eight-week-old rabbits and rats. Both the DCed ribs and the DVed ones formed bone at costal GC zone after four to six weeks. Costal cartilage zone of young rabbits and rats was DCed or DVed as stated above, and implanted into the subcutaneous pocket of abdominal wall of eight-week-old rabbits and rats. The DVed costal cartilage zone specimens formed bone after three to four weeks, but the DCed ones did not, even after eight weeks. GC cells were dissociated enzymatically from rat costal GC zone, centrifuged to be made into pellets (5 x 10(5) cells/pellet), and implanted into the peritoneal cavity of eight-week-old syngeneic rats. After four weeks, implanted GC cells formed bone. These results suggest that there are some osteogenic factors in the GC zone produced by GC cells, whose activity is lost by decalcification, and which are different from known BMPs.