Increased Serum 1,25-(OH)2-Vitamin D Concentrations Fail to Affect Serum or Urine Phosphate in Humans
Patients with recurrent calcium oxalate/apatite nephrolithiasis in association with hypercalciuria (idiopathic hypercalciuria) may exhibit low serum inorganic phosphate concentrations (1,2,3,4) in association with normal rates of urinary phosphate excretion implying the existence of impaired renal tubular phosphate reabsorption. In fact, such calcium stone formers exhibit impaired renal phosphate conservation in response to ingestion of a diet low in phosphate (5). They also exhibit higher than normal salivary phosphate concentrations (6) implying the presence of a more generalized abnormality of phosphate transport. Dietary phosphate deprivation in animals is accompanied by increased synthesis of the calcium mobilizing steroid 1,25-(OH)2-vitamin D3 by the kidney (7) and elevated serum levels of this hormone (8). Similarly renal synthesis of 1,25-(OH)2-D is increased in hypercalciuric kidney stone formers (9) and high serum 1,25-(OH)2-D concentrations among these patients may be inversely related to the degree of hypophosphatemia (4).
KeywordsIdiopathic Hypercalciuria Dietary Phosphate Urinary Phosphate Excretion Serum Inorganic Phosphate Concentration Dietary Phosphate Intake
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