Acute Actions of 1, 25-Dihydroxy-Vitamin D3in Normal Man:Effect on Calcium and Parathyroid Status

Abstract

The present study was undertaken to evaluate the acute effects of 1, 25-dihydroxy-vitamin D₃ (1, 25 (OH)₂D₃) on serum Ca, P and immunoreactive parathyroid hormone (iPTH) and urinary Ca, P, and cyclic AMP. In 8 normal subjects, samples were collected over intervals of 30 to 60 min during a control day and on a treatment day following oral ingestion of 1, 25(OH)₂D₃, 2.7 μg. For the entire group there were no significant changes in serum Ca, P, iPTH or urinary P. Urinary Ca increased significantly 7 h after administration of 1, 25(OH)₂D₃, and urinary cAMP decreased at 12 h. In 4 patients (group A), showing an increase in serum Ca by 0.2 to 0.4 mg/dl, serum iPTH decreased in 3, and the decrease in urinary cAMP appeared sooner. Among 4 patients showing no change in serum Ca after 1, 25(OH)₂D₃ (group B), 3 showed an increase in iPTH. These data document the early onset of action of 1, 25(OH)₂D₃ following its administration to normal man;increments in urinary Ca provide the most sensitive index of its action. The data provide no support for the view that 1, 25(OH)₂D₃ exerts any direct inhibitory effect on the secretion of parathyroid hormone.