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Aarskog D, Aksnes L, Markestad T: Effect of parathyroid hormone on cAMP and 1,25-dihydroxyvitamin D formation and renal handling of phosphate in vitamin D-dependent rickets. Pediatrics. 1983 Jan;71(1):59-63.
Studies were carried out to compare the effects of parathyroid extract (PTE) on the serum concentration of 1,25-dihydroxyvitamin D (1,25 [OH] 2D), 24,25-dihydroxyvitamin D (24,25 [OH] 2D), 25,26-dihydroxy vitamin D (25,26 [OH] 2D) and cAMP, and the urinary excretion of calcium, phosphorus, and cAMP in two normal adult subjects, and in a girl with vitamin D-dependent rickets. The concentration of 1,25 [OH] 2D was markedly decreased even when she was receiving a daily dose of 25,000 IU of ergocalciferol. PTE infusion resulted in a prompt and distinct increase in the serum levels and the urinary excretion of cAMP in the patient and control subjects. In the control subjects the serum concentration of 1,25 [OH] 2D increased after the PTE infusion, whereas there was no response in the patient with vitamin D-dependent rickets. The two other dihydroxylated metabolites of vitamin D showed no consistent response to the PTE infusion in the control subjects or the patient. The patient showed no phosphaturic response to PTE while she was receiving high-dosage ergocalciferol treatment. By contrast, when the patient was re-studied after therapy with 1 alpha-hydroxyvitamin D, PTE infusion resulted in an increase in urinary phosphate excretion. These findings might lend support for the notion that 1,25 [OH] 2D has an effect on tubular phosphate resorption and has a permissive role in the phosphaturic effect of parathyroid hormone. The present findings also confirm that the formation of 1,25 [OH] 2D is impaired in vitamin D-dependent rickets and indicate that the renal 25-hydroxyvitamin D-1 alpha-hydroxylase is unresponsive to the stimulatory effect of parathyroid hormone in this condition. |
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