Normophosphatemic phosphate depletion in growing rat.

To study the influence of phosphate depletion (PD) on the serum, urinary, bone, and soft tissue phosphorus, we studied growing rats given a high-phosphorus (HP), normal-phosphorus (NP), or low-phosphorus (LP) diet. We obtained the following results. a) With an LP diet, animals did not grow but developed the characteristic biochemical changes of PD. b) The NP rats had an unexplained accelerated rate of growth, and developed all the biochemical changes of PD, although they were normophosphatemic. c) Bone P and Ca were significantly lower in the LP and NP rats compared to the HP rats, suggesting that minerals were mobilized from bone to support soft tissue P needs. d) Soft tissue P was not different in HP, NP, and LP rats, confirming previous observations that soft tissue P is maintained even in PD. We conclude that 1) the physiologic adaptation to PD may occur in growing rats on an apparently normal phosphorus diet when the metabolic demand is unusually high, e.g. accelerated growth; 2) the evolution of the biochemical parameters of PD in the face of normophosphatemia suggest a sensor mechanism sensitive to change in dietary P concentration.