Stimulation of PGE2 synthesis in a co-culture of periosteal fibroblasts and osteoblast-like cells by parathyroid hormone.

In previous experiments, we demonstrated that hPTH 1-34 activates PGE2 synthesis and calcium mobilization by chick calvaria. In this report, we started to search for the PTH responsible cell population in this bone tissue. When the chick calvariae were subjected to sequential enzyme digestion, we found that the third cell population were the cells that reacted to human PTH 1-34 and bovine PTH 1-34. A subsequent procedure was performed using the cells isolated from enzyme digestion and separated into two distinct populations--periosteal fibroblasts (PF) and osteoblast-like cells (OB)--by a two-step density gradient of Percoll. We found that PF and OB cells alone did not respond to PTH in terms of PGE2 synthesis. However, when these two cell populations were mixed in the proportion of 50:50, the synthesis of PGE2 and PGF2 alpha was increased significantly by the treatment of PTH and calcitonin. No effects were demonstrated in the mixing proportions of 30:70 and 70:30. These results suggest that PTH responsiveness may need a local interaction between periosteal fibroblasts and osteoblast-like cells residing in chick calvaria.