Evidence for Preferential Effects of Parathyroid Hormone, Calcitonin and Adenosine on Bone and Periosteum1

Abstract

In order to explore the distribution of hormone-responsive cells in skeletal tissues, the effects of synthetic bovine parathyroid hormone N-terminal peptide (bPTH 1-34) and salmon calcitonin (sCT) were examined on cyclic[c]AMP levels in periosteum-free rat calvaria, segments of periosteum and in isolated cells dispersed from each tissue by collagenase digestion. Synthetic bovine PTH increased cAMP levels to a greater degree in calvaria and in isolated bone cells than in the periosteal segments and cells, whereas sCT was more effective in the periosteal than in the bone systems. Primary cultures prepared from bone and periosteal cell populations exhibited progressive increases in their responsiveness to bPTH (1-34) and progressive decreases in responsiveness to sCT. After 6 days in the culture, bone cells failed to respond to sCT, and sCT did not modify their response to simultaneously added bPTH (1-34). Six-day periosteal cell cultures exhibited residual sCT responsivity and an additive response upon simultaneous exposure to high concentrations of bPTH (1-34) and sCT, suggesting separate sites of hormone action. Adenosine, a known stimulator of bone cell adenylylate cyclase, caused a greater increase in periosteal cell than in bone cell cAMP. bPTH (1-34)-responsive cells which enrich periosteum-free bone may be osteoblasts, in view of their histological prominence in this tissue and in the bone cell isolates. Periosteal cells which responded to sCT and to adenosine preferentially are unidentified. Although periosteal segments contained numerous fibroblast-like cells, skin fibroblasts cultured from the same fetuses were sCT-insensitive. Growth in primary culture appears to alter the number of hormone-responsive cells or responsiveness of existing cells to each hormone, or both.