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Acute Actions of 1, 25-Dihydroxy-Vitamin D₃ in Normal Man:Effect on Calcium and Parathyroid Status

Medical and Research Services of the VA Wadstvorth Hospital Center and the Department ofMedicine, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California, Department of Medicine, University of Miami School of Medicine, Miami, Florida, and Departmentof Biochemistry, University of California, Riverside, Riverside, California

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.

¹ Clinical Investigator of the Veterans Administration.

² Present address: Division of Nephrology, Los Angeles County-University of Southern California Medical Center, Los Angeles, California.

Supported in part by NIH grants AM-14750, AM-5383 and AM-16768, and by research funds from the Veterans Administration.

Received June 14, 1976.

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