Changes in lipids during matrix: induced endochondral bone formation.

The changes in lipids occurring during the process of endochondral ossification have been characterized by studying the discrete phases of matrix-induced endochondral bone formation in the rat. Calcium-acidic phospholipid-phosphate complexes were shown to increase in concentration during cartilage calcification (day 9) and to peak in content during early bone formation (days 11-13), the times during which the rate of mineral deposition, as indicated by the change in ash weight was greatest. These data support the hypothesis that the calcium-acidic phospholipid-phosphate complexes play a role in the in vivo initiation of hydroxyapatite deposition. The overall lipid composition of the induced matrix newly formed cartilage (days 7-9) was comparable to that of normal cartilage, with the phospholipid composition matching that of chondrocyte plasma membranes. Times of vascular invasion and formation of marrow cavities were marked by elevated total lipid and triglyceride contents.