PEDIATRICS Vol. 71 No. 1 January 1983, pp. 59-63
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Effect of Parathyroid Hormone on cAMP and 1,25-Dihydroxyvitamin D Formation and Renal Handling of Phosphate in Vitamin D-Dependent Rickets

Dagfinn Aarskog MD1, Lage Aksnes PhD1, and Trond Markestad MD1

1 From the Department of Pediatrics, University of Bergen, Bergen, Norway

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 lagr-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-lagr-hydroxylase is unresponsive to the stimulatory effect of parathyroid hormone in this condition.

Key Words: vitamin D-dependent rickets • 1,25-dihydroxyvitamin D • parathyroid hormone • cAMP • phosphate

Submitted on December 28, 1981
Accepted on March 29, 1982