Changes in red cell, plasma, inulin, and total water compartments in rat femurs. Comparison of vitamin D deficiency and diphosphonate induced rickets.

The vascular space, as measured with the use of 99m-technetium-labelled red cells and 131I-serum albumin, as well as the 14C-inulin and 3H2O fluid compartments were measured in rats which had been made rachitic by the use of a low phosphate vitamin D-deficient diet. A similar group of rachitic animals fed vitamin D2 50 IU, 5 and 3 days prior to sacrifice and a weight-matched control group were also studied. The same spaces were measured in rats made rachitic by daily s.c. injections of ethane-1-hydroxy-1,1-diphosphonate (EHDP) for 4 weeks and a weight-matched saline injected control group. Findings indicated that the red cell and RISA spaces were unchanged in the untreated D-deficient group as compared to controls but increased after being repleted with vitamin D. By contrast, the vascular space was depressed in the EHDP-treated group. The water content was elevated in D-deficient rickets returning towards normal on healing, whilst both inulin and water spaces were increased in the EHDP-treated animals. Thus, while the extravascular space reflected the presence of osteoid, the vascular space depended on cellular turnover and the process of mineralization.