Influence of vitamin D status on the content of complexed acidic phospholipids in chick diaphyseal bone.

Calcium acidic phospholipid phosphate complexes cause hydroxyapatite formation in vitro and in vivo. Previous studies have shown that the amount of these complexed acidic phospholipids is altered in the bones of animals depleted of vitamin D and phosphate. To help differentiate the effects of vitamin D from those due to altered mineral metabolism, the amount of complexed acidic phospholipids present in diaphyseal bone was determined in five groups of chicks varying in calcium, phosphate and vitamin D status. Highest levels of complexed acidic phospholipids were found in chicks receiving vitamin D and having normal serum levels of Ca and P. Lowest levels were found in vitamin D-deficient chicks; levels were not altered in vitamin D-deficient chicks when their serum Ca was normalized. Intermediate levels were found in vitamin D-treated chicks fed a low Ca diet. Levels of the complexed acidic phospholipids were low in bones of hypophosphatemic, vitamin D-treated chicks but, when related to total lipid phosphorus content, values were similar to those of hypocalcemic chicks. These data suggest that while disturbances in calcium and phosphate metabolism which are present in rickets influence the bone content of these complexed acidic phospholipids, vitamin D may also play a direct role in their formation. Further, the ability of vitamin D to increase bone complexed acidic phospholipid content does not seem to be related to its hypercalcemic effect.