Regulation of calcium absorption by 1,25,dihydroxy-vitamin D-Studies of the effects of a bisphosphonate treatment

In 10 patients with Paget's disease of bone and 2 patients with osteoporosis, we studied the effects of hypocalcemia and hypophosphatemia induced by disodium-(3-amino-1-hydroxypropylidene)-1,-bisphosphonate (APD) treatment on the serum concentration of PTH and 1,25-dihydroxyvitamin D [1,25(OH)₂D₃] and on calcium absorption and balance. The fall in serum calcium and phosphate was associated with a rise in the serum concentration of PTH and 1,25(OH)₂D₃, coupled with increases in net calcium absorption and calcium balance. The concentration of 1,25(OH)₂D₃ was significantly related (P<0.001) to the serum calcium (r=0.66), the serum phosphate (r=0.78), and the serum PTH (r=0.71), confirming the interrelated control of these parameters on 1,25(OH)₂D₃ production. Moreover, the rise in 1,25(OH)₂D₃ caused an appropriate rise in calcium absorption (r=0.74) and calcium balance (r=0.86), showing that this vitamin D metabolite contributes as a hormone to calcium homeostasis.