Abstract
Radioisotopic studies have recently shed some light on the bone formation rates in various disease states. Using Ca-45, Bauer et ale (1), in Sweden, and Heaney (2), at the National Institute of Health, devised a method of determining rate of calcium deposition in various diseases. By their technique so-called "bone formation rates" in Paget’s disease and in clinical abnormalities of thyroid function showed their expected aberrances from normal. In osteoporosis, however, seven patients thus far studied have shown rates in the normal range. Similarly normal rates in osteoporosis have since been reported by Nordin (3). This finding raises the possibility that increased bone resorption may contribute to the diminished bone mass in osteoporosis. | The present studies were undertaken to see whether the rate of bone resorption could be defined and whether it was possible to relate variations of the responses to different states of bone metabolism. In an attempt to establish the existence and extent of homeostatically regulated bone resorption, human subjects were studied by means of a low dose, long term, intravenous calcium infusion delivered by a constant infusion pump. The rate of exogenous calcium replacement was varied from patient to patient and serially from study to study in the same patient. The data collected made it possible to calculate the amount of calcium retained. The extent of this calcium retention is dependent on the following three points: | 1. Suppression of bone resorption. | 2. Expansion of extraosseous calcium compartments. | 3. Altered calcium clearance in the kidney secondary to changes in parathyroid function. By varying the rates of infusion and by following manifestations of altered parathyroid function, an attempt was made to quantitate the suppressible rate of bone resorption. This was not achieved with certainty but certain homeostatic changes of calcium and phosphate metabolism were found in all studies.