Parathyroid Hormone, Carbonic Anhydrase and Calcium Homeostasis
Changes in the concentration of extracellular ionized calcium (Ca2+) regulate the secretion of parathyroid hormone (PTH) and calcitonin (CT) and vice versa in a very fast and effective way. Most of the biochemical reactions involved in these processes are still unknown. There is some knowledge about the way these hormones are synthesized and secreted (Mac Gregor and Cohn 1978), but it is still not known how the extracellular Ca2+ signal is recognized and how this event is then transformed into an intracelullar message that modulates hormone secretion. Undoubtedly, the osteoclast’s resorbing activity is enhanced by PTH (Gaillard et al. 1979), but it is still not clear, whether the osteoclast is a target cell for this hormone (Jilka 1986). Because of the lack of PTH receptors on the osteoclast surface this stimulation may be mediated through osteoblasts (Rodan and Martin 1981).
KeywordsOsteoporosis CaCl2 Dexamethasone Epinephrine Apatite
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