IN VITRO STUDIES OF BONE RESORPTIVE MECHANISMS 565 



VITAMIND PTE CORTISONE 



+ 20 



20 



1 



□ co 



I I 



+ 20 



-2 C 



Fig. 5. Differences in final medium calcium and phosphorus concentrations 

 from simultaneously incubated controls following treatment with vitamin D, 

 parathyroid extract, or cortisone. Calvaria from mice 7 to 9 weeks old were 

 used in all experiments. Animals were prepared as follows: In the vitamin D 

 experiments, 4-week-old mice were placed on a vitamin D-free synthetic diet 

 containing approximately 1 per cent Ca and 1 per cent P for 3 to 4 weeks. 

 Those treated with vitamin D received a single dose of 8000 units 3 days prior 

 to sacrifice. Animals that had received no vitamin D served as controls. The 

 data for parathyroid extract treatment have been recalculated from Fig. 4. 

 Cortisone acetate 2.5 mg was injected subcutaneously in normal mice daily 

 for 8 days preceding sacrifice to give the changes seen in the last section of 

 the diagram. Conditions of incubation, etc., were as in Figs. 2, 3, and 4. (These 

 data have been recalculated from Schartum and Nichols, 1961a; Schartum 

 and Nichols, 1961/?; and Nichols et al, 1963.) 



ments — were almost entirely a reflection of change in mineral solu- 

 bility. 



It is of great interest that alteration in mineral solubility rather 

 than the fraction dependent on cell metabolism seems to determine 

 these changes in Ca and P distribution, at least as seen in this in 

 vitro model. So far we have found only one case where this is not 

 true : in a mutant strain of rats which lack the ability to resorb bone 

 yet have normal serum Ca concentrations, low serum P, and ap- 

 parently normal parathyroids (Vaes and Nichols, 1963). Figure 6 

 shows that the Ca level maintained by inactive bone from normal 

 and ia rats, as this strain has been named (Creep, 1941), is the 



