Involvement of Phosphodiesterase I in Mineralization: Histochemical Studies Using Antler from Red Deer (Cervus elaphus) as a Model

The growing antler of 1-year-old red deer is an excellent system in which to study processes involved in ``cartilage model'' endochondral-type bone growth. Antlers grow from the tip, permitting the developmental sequences of bone formation to be studied as distance-dependent phenomena, in which early processes can be observed at the distal end, and later events are sequentially more proximal. Quantitative light microscope histochemical assays for alkaline phosphatase (ALP) and phosphodiesterase I (PDE I) were used to determine the activities of these two phosphohydrolases in relation to antler mineralization and remodeling. Both enzymes were absent in proliferating young cartilage near the end, but progressively increased in activity in a proximal direction. ALP levels were maximal when mineralization was just beginning, whereas PDE I activity was greatest more proximally, where mineralization was more complete. This study provides strong indirect evidence that each of these enzymes has a function in mineralization, but that their roles are not identical.