Induction of normal and dystrophic mineralization by glycerophosphates in long-term bone organ culture.

The effectiveness of Na-beta-, and Ca-glycerophosphates (GPs) in inducing mineralization was tested during long-term organ culture of femurs from 14-day-old chick embryos. When bones were incubated with Na-GP, a 66% rise in inorganic phosphate level was measured in the medium, supporting the notion that provision of a substrate for alkaline phosphatase (ALP) increased available phosphate. On the other hand, if the concentrations of Ca2+ were raised, available inorganic phosphate was decreased. Similarly, increases in inorganic phosphate decreased available calcium. Both GPs induced mineralization in bone and cartilage, but more matrix was mineralized with Ca-GP. However, the induction of mineralization by GPs was accompanied by dystrophic calcification, reduction of matrix formation and ALP activity, and increased release of lactate dehydrogenase into the culture medium. The new osteoid, which formed during culture, mineralized in the absence of GPs without the above adverse effects provided the culture period was longer than 15 days. The described organ culture system therefore facilitates studies of the mechanism of bone mineralization without the disadvantages of GP addition.