Effect of Parathyroid Hormone on Vitamin D Metabolism in Osteopetrosis

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Abstract
Indices of vitamin D metabolism were studied before and after infusion of bone parathyroid hormone extract in 3 children with osteopetrosis. Basal serum concentrations of Ca, alkaline phosphatase and 25-hydroxyvitamin D tended to be low. Serum immunoreactive parathyroid hormone levels were in the upper normal range in 2 patients. A marked increase in urinary cAMP in all patients was solely due to an increase in the nephrogenous cAMP. The basal concentration of 1,25-dihydroxyvitamin D was clearly more than the upper limit of normal range in all 3 patients and increased after parathyroid extract infusion in 1 patient. The basal serum levels of 24,25-dihydroxyvitamin D were within normal limits and tended to decrease after parathyroid extract infusion in 2 of the patients. Parathyroid hormone and 1,25-dihydroxyvitamin D act in concert to increase Ca resorption from bone, and the increased serum levels of both these factors may reflect lack, or unresponsiveness, of target cells in bone.