Effect of calcitonin on calcium and magnesium transport in rat nephron

Renal calcium and magnesium reabsorption was investigated in young, thyroparathyroidectomized rats receiving synthetic salmon calcitonin. Kidney and tubular function was assessed by clearance and in vivo microperfusion techniques, respectively. Calcitonin reduced urinary calcium and magnesium excretion that was attributed to increased reabsorption within the loop of Henle. This enchanced reabsorption was independent of parathyroid hormone; however, it is contingent on a decline in plasma calcium concentration. Prevention of hypocalcemia by CaCl2 infusion in rats acutely administered calcitonin resulted in loop function comparable to animals not receiving the hormone. Calcitonin had little effect on proximal tubule or distal tubule electrolyte reabsorption. These results are consistent with a transport model for calcium and magnesium in the loop of Henle involving a contraluminal transfer step modulated by absolute extracellular calcium or magnesium. Furthermore, these studies suggest that the discrepancies present in the literature concerning renal effects of calcitonin on electrolyte reabsorption are due to variations in observed hormone action, namely, the effect on plasma calcium concentration.