Abstract
Previous investigations in this laboratory have been directed toward denning the parameters of plasma calcium homeostasis (1,2). The data obtained support the hypothesis that plasma calcium is maintained by two processes. The first is a basic equilibration process which appears to be a continuous attempt to bring the calcium ion into equilibrium between bone and blood. The second is a hormonal process by which a continuously secreting parathyroid gland maintains the normally observed circulating calcium values above the basic level by influencing bone resorption. Osteoclastic activity has been correlated with this second process(3), though not proven necessary for hormonal action. These studies and conclusions are based on the prevention of a drop in plasma calcium below normal levels and are not necessarily related to the problem of the existence of a second parathyroid hormone, calcitonin, which has been postulated to be concerned with prevention of hypercalcemia(4).
Whether or not the solubility of the bone crystal could be affected in vivo was investigated by Talmage and Kraintz(2) using aci-dotic animals. Such treatment increased the amount of calcium removed by peritoneal lavage in the parathyroidectomized rats. In contrast, subsequent studies showed that administration of sodium fluoride by peritoneal lavage decreased the amount of calcium removed by this procedure(5). The investigations reported here are a continuation of the NaF studies and were carried out to clarify whether or not the decreased calcium levels observed in animals receiving sodium fluoride were a consequence of a reduction in solubility of the hydroxyapatite crystal of bone. Such an effect of fluoride on bone crystal has been suggested by others (6,7).
Materials and methods. A description of the technique of peritoneal lavage and of the constituents of the buffered, isotonic lavage fluid has been given(8).
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