. Calcified tissues; proceedings. Bone; Collagen; Calcification. Some Observations on the Nature of Bone Mineral 141 In each case there are high values in the young which fall to a minimum around the age of 40 before a further rise in later years. The general trend is highly suggestive. It is interesting to speculate that in osteomalacia where the mineralisation of osteoid is retarded, the observed low phosphate concentrations may be the result rather than the cause of the condition, although in several cases secondary hyper- parathyroidism with increased renal clearance of phosphate may also
. Calcified tissues; proceedings. Bone; Collagen; Calcification. Some Observations on the Nature of Bone Mineral 141 In each case there are high values in the young which fall to a minimum around the age of 40 before a further rise in later years. The general trend is highly suggestive. It is interesting to speculate that in osteomalacia where the mineralisation of osteoid is retarded, the observed low phosphate concentrations may be the result rather than the cause of the condition, although in several cases secondary hyper- parathyroidism with increased renal clearance of phosphate may also be a factor. In carefully controlled experimental conditions, however, it may be that a critical evaluation of plasma phosphate levels will indicate the trend in the rate of new bone formation. In conclusion, I would like to commend caution to those workers who assess "calcification" and "calcifiability" in vitro. Dr. H. Fleisch has kindly made available his data on the "formation products" of calcium phos- phate precipitation on to collagen in vitro. The ap- propriate calculations for de- termining the stoichiometry of the equilibrium at the point oi precipitation have been made using the chemi- cal potential method as de- scribed in MacGregor and Brown (1965). The results are shown in Fig. 3. A good fit was obtained and the regression coefficient was such that the Ca : P ratio of the equilibrium was not si- gnificantly different from 1 (in fact Ca : P = : 6). In this case, therefore, CaHP04 must have been the dominant phase, and not the OCP or HA found when bone is present. It may be of interest here to mention in parenthesis that an unselected group of renal calculi equilibrated at pH 7 in vitro have also shown the presence of OCP (MacGregor et al., in press). It appears probable that the precipitation of inorganic Ca and P in the absence of formed bone or an "active" template does not represent either the process of in vivo calcif
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