Urinary hydroxyproline excretion in phosphate depleted rachitic rats

Nutritional rickets: thoughts about pathogenesis

The pathogenesis of nutritional rickets is not well-understood. While the etiologies include deficiencies of vitamin D, calcium (Ca) or phosphate (PO4), and perhaps aluminium toxicity, the role these nutrients play in the development of tissue level anomalies characteristic of rachitic cartilage and bone has yet to be defined. Reported alterations in the biochemistry of rachitic bone and cartilaginous matrix which could adversely affect mineralization and endochondral ossification are of questionable significance since the tissues mineralize rapidly when exposed to Ca and PO4 salts in vivo and in vitro. The low Ca and PO4 concentrations of the extracellular fluid (ECF) bathing rachitic cartilage and bone matrix suggest that local mechanisms operate to impair mineralization. In healing rickets, the Ca and PO4 content of these tissue fluids increases in the same time-frame it takes to experimentally remineralize the matrices. However, it is not certain what determines the Ca and PO4 content of the ECF. Cytokines which may play a role in the cellular regulation of Ca and PO4 and maintain processes which contribute to normal patterns of endochondral ossification could provide a mechanism common to the pathogenesis of rickets from a variety of causes.

Changes in organic matrix of bone and of bone and blood ATP in rats fed rachitogenic diets

Vitamin D deficient and phosphate deficient states were produced in young rats by the use of synthetic diets. Whole blood ATP, serum calcium and phosphorus and the ash, phospholipid, hexosamine and hydroxyproline contents of metaphyseal bones of control and rachitic rats were measured after 4 weeks on the diets. There was a decrease in whole blood ATP and serum phosphorus of the rachitic rats, and in the contents of ash, phospholipid and hexosamine of the rachitic metaphyses, while the hydroxyproline contents of the rachitic bones were higher than those of the controls. Subcutaneous injection of ATP or inorganic phosphate in rats, fed a low phosphate diet deficient in vitamin D, caused an increase in serum phosphorus and blood ATP levels and in metaphyseal ash contents. It is suggested that some of the metabolic disturbances in rickets are due to alteration in ATP production.