The effect of short-term treatment with vitamin D metabolites on bone lipid and mineral composition in healing vitamin D-deficient rats

Vitamin D deficiency is known to cause alterations in the lipid and mineral components of bone and cartilage. In this study, second generation, normal phosphatemic, vitamin D-deficient rats, treated with low and high doses of three different vitamin D metabolites were sacrificed 24 h after treatment and their bones analyzed in order to determine which metabolites were most effective in altering the lipid composition. In the untreated vitamin D-deficient rats, tissues undergoing endochondral ossification (epimetaphyses), periosteal and endosteal bone formation (diaphyseal bone), and intramembranous bone formation (calvaria) all contained lower amounts of complexed acidic phospholipids, as well as decreased amounts of mineral. Twenty-four hours following treatment, the complexed acidic phospholipid content was significantly increased relative to both untreated and normal (vitamin D-replete) animals, the greatest increases occurring in animals treated with 1,25-dihydroxyvitamin D. All metabolites tested altered histomorphometric and/or mineral parameters, but only 1,25-dihydroxyvitamin D, in low and high doses, significantly increased the content of the complexed acidic phospholipids in all tissues studied. High doses of other metabolites increased complexed acidic phospholipid content in some tissues, perhaps due to their conversion to 1,25-dihydroxyvitamin D. Linear relationships between serum 1,25-dihydroxyvitamin D levels and tissue complexed acidic phospholipid content are reported. It is suggested that one way in which this metabolite may directly contribute to calcification is by facilitating formation of lipids involved in this process.