These studies provide the first evidence that parathyroid hormone (PTH), calcitonin (CT), and insulin, all known effectors of bone cell metabolism, stimulate the activity of guanylate cyclase in osteogenic cells derived from fetal mouse calvarial mesenchyme. Adenylate cyclase activity was stimulated by PTH and epinephrine, but not by CT, the latter effect being consistent with an absence of osteoclastpprogenitor cells in this osteogenic mesenchyme. Adenylate cyclase activity was associated entirely with the particulate fraction of the cells while guanylate cyclase, as well as acid and alkaline phosphatase, were present in both soluble and particulate material. The activation of guanylate cyclase by hormones may provide a better basis for understanding the differentiation and regulation of osteogenic cells.
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