Ectopic bone formation and aging.

Six-week-old, 6-month-old, and 2-year-old female rats of the Wistar strain were implanted with decalcified bone powder prepared from rats of the same strain. An encapsulated deposit of cartilage and bone formed. The deposits were removed at intervals and studied histologically and after administration of 45Ca. Intramembranous bone formed in 14 days in the 6-week-old animals, but was not seen until the 23rd day in the 2-year-old rats. This implant system may provide a model for the study of the mechanisms for the decline of osteogenesis, or the low bone formation rate which occurs with aging.

Interrelations of matrix lipids, vesicles, and calcification.

When calcifying tissues were extracted with hot pyridine or hot benzene and then decalcified and stained with Sudan black B, the areas where mineralization was being initiated stained strongly, the rest of the calcified tissues being unstained. Histochemical methods showed that lipids were responsible for the staining. They were isolated biochemically and found to be phospholipids, very resistant to extraction before decalcification of the tissues and consisting predominantly of phosphatidyl serine and phosphatidyl inositol. It was proposed that these phospholipids were active at nucleating sites in apatite crystal formation, since it is known that phosphatidyl serine binds calcium strongly. It has been shown that phosphatidyl serine is present in matrix vesicles.