Vit. D and Citrate Metabolism. Inhibition of Vit. D Effect by Cortisol.

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Abstract
Correlation of the effect of vitamin D in augmenting concentrations of citrate in plasma and bone with its antirachitic action was studied. Rats were made rachitic by feeding a vitamin D-deficient diet which was also low in available P. Addition of cortisol to the diet of such rats reduced concentration of citrate in serum and also blocked the effect of vitamin D in increasing serum and bone-citrate levels. Antirachitic action of vitamin D as measured by rise of serum P concentrations and by histological evidences of calcification of rachitic cartilage and osteoid was not suppressed by cortisol. The antirachitic action of vitamin D and its effect upon citrate metabolism can, therefore, be separated. The tibias of vitamin D deficient cortisol fed rats show evidences of increased calcification in comparison with rachitic controls which might in part be due to inhibition of bone resorption as well as retardation of cartilage growth by cortisol. This increased calcification in cortisol fed rats is associated with extreme depletion of extracellular phosphate.