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, we have examined the effects of synthetic bovine parathyroid hormone N-terminal peptide (bPTH 1-34) and salmon calcitonin (sCT) on cyclic 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 cyclic AMP 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 six days in the culture, bone cells failed to respond to sCT, and sCT did not modify their response 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 adenylyl cyclase, caused a greater increase in periosteal cell than in bone cell cyclic AMP. 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.

Bone formation and calcification by isolated osteoblastlike cells.

“…Most of the evidence for this property is, however, circumstantial . A number of investigators have found high cAMP responses to PTH in isolated bone-cell populations where the osteoblasts were expected to be (13, 17,21,24). A more direct indication was provided by Davidovitch et al (5), who showed with immunohistochemical techniques that, in osteoblasts, cAMP can be stimulated by PTE .…”

“…Several procedures have been used to obtain these different types of bone cell (13,17,20,21,23) . Generally, the isolated cells are cultured as a monolayer for a number of days and then used for biochemical studies.…”

Effect of insulinlike growth factor I on DNA and protein synthesis in cultured rat calvaria.

“…Because the stimulatory effect of IGF I on CDP labeling was opposedI by IBMX, a knowni inhibitor of cyclic AMP (cAMP) phosplhodliesterase (34), and by PTH, believed to acet onl bone by inereasing cAMP (14,23), it is possible that the effect of IGF I on collagen syntlhesis is medliatedl by a dlecrease in cAMP. This mechaniisnm has been proposed for other growtlh fhactors (35), but cAMP hals nlot been reportedl to h1ave a role mediatinig IGF effects in other tisstues or cell systemiis ancd the IGF I effeets on [3Hlthymidine incorporationi in bone were not altered by IBMX.…”

Development of parathyroid hormone- and calcitonin-activated adenylate cyclases in embryonic chicken limb and in cultured cells from embryonic chicken limb.

“…Additional analysis of the enzymatic content and responsiveness to PTH and CT suggested that the PT cells are osteoblasts (4). Independent studies in Peck's laboratory using a mechanical separation technique also showed that adenylate cyclase of -osteoblasts is activated by PTH and not by CT, whereas CT-stimulated production of cyclic AMP is observed in a separate cell population obtained from the periosteum (5). These important findings suggested to us the possibility that, by assay of the hormonally activated adenylate cyclases in developing bone tissue, it should be possible to delineate the temporal relationships for appearance of osteoblasts and osteoclasts and to define enzymatically the emergence of bone cells.…”