Effect of Growth Hormone Administration: Reciprocal Changes in Serum lα,25-Dihydroxyvitamin D and Intestinal Calcium Absorption*

The mechanism by which GH stimulates intestinal calcium absorption was explored. In this study, seven children with idiopathic GH deficiency were studied before and during GH therapy while they were maintained on the same metabolic diet. After 5-14 months of GH administration, fractional intestinal calcium absorption increased from 0.364 +/- 0.114 to 0.449 +/- 0.159 (P less than 0.01), and serum 1,25-dihydroxyvitamin D decreased from 63.7 +/ 19.3 to 46.7 +/ 17.8 pg/ml (P less than 0.025). Serum immunoreactive parathyroid hormone, urinary cAmp, serum 24,25-dihydroxyvitamin D, and 25-hydroxyvitamin D did not change significantly. The data suggest that GH does not directly influence parathyroid hormone or vitamin D metabolism. The possibility that relative intestinal resistance to 1,25-dihydroxyvitamin D exists in patients with GH deficiency is considered.