REGULATION OF RENAL CALBINDIN-D28K - THE ROLE OF CALCITONIN

Infusion of calcitonin lowers circulating calcium, but in the distal t ubule of the kidney, pharmacological doses of calcitonin increase the active calcium reabsorption. Calbindin-D28k plays a significant role i n the calcium reabsorption in the distal convoluted tubule of the kidn ey. The effect of calcitonin on renal calbindin-D28k in relation to ca lcium metabolic changes was therefore examined. In study 1, thyroparat hyroidectomy followed by autotransplantation of the parathyroid glands (TX) was compared with a sham operation in rats, TX reduced plasma ca lcitonin from 54 +/- 2 to 9 +/- 1 pg/ml (P < 0.001), whereas ionized c alcium and parathyroid hormone were returned to the control value afte r an initial decrease, indicating a successful implantation of the par athyroid glands. No changes were seen in calbindin-D or plasma 1,25(OH )(2)D. In study 2, subcutaneous infusion of salmon calcitonin 2.5 U/kg /hour via osmotic pumps was compared with infusion of vehicle in rats. Ionized calcium was reduced from 1.37 +/- 0.01 to 1.33 +/- 0.02 mmol/ liter (P < 0.05), whereas no changes were seen in renal or intestinal calbindin-D or in plasma 1,25(OH)(2)D. After TX, only calcitonin decre ased whereas the other calcium metabolic parameters showed no change. This indicates that in rats, selective elimination of calcitonin does not influence other parameters of the calcium metabolism and that the effect of calcitonin on calcium transport in the distal tubule is not mediated via an increase in renal calbindin-D28k.