Parathyroid function and vitamin D metabolism during human growth hormone replacement

Changes in calcium and phosphorus metabolism were studied in nine children with GH deficiency before and during human GH replacement therapy. Parathyroid function and serum concentrations of physiologically important vitamin D metabolites were examined to determine their relationship to changes in mineral metabolism. By comparison with pretreatment values, the GH-treated children showed significant increases in growth rate and renal tubular phosphate reabsorption and a significant decrease in urinary calcium excretion after a standardized oral load. There was no significant change in serum concentrations of parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, or 24,25-dihydroxyvitamin D or in nephrogenous cAMP excretion. Although GH has been proposed as a regulator of vitamin D metabolism, the present study demonstrates that the anabolic changes in calcium and phosphorus metabolism accompanying GH therapy are not mediated via changes in parathyroid hormone or vitamin D status.