140 



J. MacGregor 



data. However, if it is true that OCP is present then, being more reactive than 

 hydroxyapatite, the ion product representing its stoichiometry should be more con- 

 stant than any other possible products at equilibrium. I have calculated the various 

 ion products for the child bone data along with their distributions, standard errors 

 and coefficients of variation. These data are shown in the following Table: 



It is clear from the coefficients of variation that the OCP product is undoubtedly 

 the most constant of the "equilibrium constants", and the presence of OCP in the 

 bone powder is confirmed. 



If new bone mineral is laid down as OCP then even in the adult a proportion of 

 the skeleton must react as OCP with consequent elevation of the equilibrium ion 

 product in terms of Ca** and P""~. As the parathyroid glands specifically ensure the 

 constancy of (Ca"^^}, it follows that variations in the rate of new bone formation 

 (and hence the proportion of OCP) might be expected to result in variations in 

 plasma inorganic phosphate levels. Certainly a raised plasma inorganic phosphate is 

 a feature of acromegaly and low values are found in hypopituitarism (Astwood, 



1955). Studies with human 

 growth hormone (Gershberg, 

 1960) have also shown that the 

 administration of the hormone 

 is accompanied by a prompt 

 rise in plasma inorganic phos- 

 phate concentration. 



There have recently been 

 many developments in quanti- 

 tative histology. Frost has vig- 

 orously led the field and has 

 associated active bone forma- 

 tion with many parameters, 

 such as the number of foci of 

 formation per mm"' (Frost, 

 1964), the number of "active 

 seams" per mm- (Frost, 1963), 

 the percentage of live osteo- 

 cytes (Frost, 1963). The last 

 two of these parameters have 

 redrawn from Frost's data and 

 are shown in Fig. 2. Also shown is the mean regression line of inorganic phosphate, 

 concentrations (y) on age (x) in normal women (Greenberg et a!., 1960): 



logio y = 0.73072 - 0.009610 x - 0.000102 x- + 0.016700 log,o x 



^1 





0.^-^ 



20 



Age Years 



Fig. 2. The relationship of 



osteoid seam count (/\) 



organic phosphate 



U lining osteocytes (o), and acti 

 vith regression curve of plasma i 

 concentration and age (>') 



