Phosphorus adaptation in rats in absence of vitamin D or parathyroid glands

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Abstract
Growing rats even when vitamin D deficient became adapted to Pi deficiency by increasing absorption and minimizing excretion. Feeding low-Pi diet for 3 wk reduced urinary Pi by 80% (P < 0.001) and urinary 32P by 50% (P < 0.001). Low Pi regimen increased 32P absorption from a 32P-labeled meal by 50% (P < 0.001), even when the animals were vitamin D deficient or thyroparathyroidectomized. The marked increase in retention of 32P in P-deficient rats could not be accounted for by decreased endogenous intestinal excretion plus increased kidney reabsorption; increased intestinal absorption played a part. 32P absorption was significantly reduced (P < 0.001) by vitamin D deficiency in rats fed control diet (0.6%) Pi or low-Pi diet (0.03%). Endogenous intestinal or urinary excretion of 32P was unaltered by vitamin D deficiency. There are 2 mechanisms for P adaptation: kidney retention not requiring vitamin D and increased intestinal absorption of Pi not requiring parathyroids, thyroids or vitamin D.