Differential biological effects of calcitonin and parathyroid hormone on isolated perfused bone

These studies examine the release of 3',5'-cyclic adenosine monophosphate (cyclic AMP) from isolated perfused canine bones in response to synthetic bovine parathyroid hormone (syn b-PTH 1-34) and human calcitonin (hCT). Bones for perfusion were obtained from three groups of dogs: control (n = 11); thyroparathyroidectomized (n = 7), and mithramycin-treated thyroparathyroidectomized animals (n = 5). The results indicate that PTH causes a greater release of cyclic AMP from adult bones than CT; the addition of the two hormones simultaneously results in a synergistic rather than an additive effect; mithramycin inhibits the cyclic AMP response to calcitonin; and thyroparathyroidectomy decreases the cyclic AMP release in response to CT stimulation, suggesting that the cells (osteoclast-like) that respond to CT have an impaired response in the absence of PTH; acute TPTX does not affect the response of the cell populations of adult bones to PTH.