Comparison of bone formed intramuscularly after transplantation of scapular and calvarial osteoblasts.

Previous work suggested that osteoblasts determine the size of the bone marrow area within the bone and that calvarial osteoblasts differ from those induced intramuscularly by cartilage formed by transplanted epiphyseal chondrocytes. This study reports morphological observations of bone formed by transplanted scapular and calvarial osteoblasts isolated from bones of young rats. In intact scapulas of 28-day-old rats the percentage area occupied by bone tissue in relation to bone marrow was 6 times larger than in parietal bones of comparable age. Isolated syngeneic scapular osteoblasts usually produced an ossicle with similar general structure and ratio bone tissue/bone marrow area as in intact scapulas. In transplants of calvarial osteoblasts numerous islands of bone tissue with a small amount of bone marrow appeared. Bone formed in allogenic transplants was rejected. These results suggest that osteoblasts from endochondral scapular bone may have different properties than those from intramembranous calvarial bones. Alternatively, the large amount of medullary space in bone produced by transplanted scapular osteoblasts could result from their contamination with bone marrow stromal cells.