Phospholipid changes in the bones of the vitamin D-deficient, phosphate-deficient, immature rat

The epiphyseal (cartilage) and diaphyseal (bone) regions of the long bones of vitamin D-deficient, phosphate-deficient, immature rats have been shown to contain Ca-PL-PO4 complexes in amounts comparable to that found in normal rat bones. This suggests that these calcium acidic phospholipid complexes are formed prior to mineralization. The metaphysis (bone and calcified cartilage) of the experimental animals contained less Ca-PL-PO4 than control bone, which suggests that Ca-PL-PO4 content is elevated as mineralizing activity increases. Overall bone lipid composition was dependent on the vitamin D status of the animals. Total lipid, cholesterol, and cholesterol ester content was higher in experimental animals than in controls. In contrast, free fatty acid and lysophosphatide were lower in experimental than in control animal's bones. The total phospholipid content (based on organic phosphate analyses) was unaltered by the vitamin D status. These lipid changes, reminiscent of changes seen in the intestinal brush border membrane of rachitic animals, suggest that vitamin D effects on lipid metabolism in bone may be similar to those in the intestine.