The Influence of Endogenous or Exogenous Calcitonin on Daily Urinary Calcium Excretion1

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Abstract
The effect of removal of the thyroids, and of calcitonin (CT) infusion, on urinary Ca values was studied in the rat. Ca infusion into thyroidectomized rats bearing functional parathyroid transplants (PTT-TX) resulted in urine Ca values 10 to 20-fold greater than those following similar infusion to normal rats or to PTT-TX rats also infused with CT. Daily renal excretion of Ca was determined in PTT-TX rats fed normal or restricted amounts of laboratory rat chow, and compared to that of normal rats and of rats with intact thyroid glands and transplanted parathyroid glands. The absence of the thyroid glands resulted in a daily renal excretion of Ca which was approximately 0.5 mg greater than control values. Injection of salmon CT into PTT-TX rats during the period of active feeding reduced the urinary Ca excretion to normal for the first 24 h collection period. Continued daily injections of this hormone reversed this effect, and by the 3rd day, caused an increased renal Ca excretion. It is suggested that secretion of endogenous calcitonin during feeding in the rat results in a conservation of Ca by the animal. The amount conserved is of such a small magnitude that time would be required to develop beneficial effects for the animal. The excessive Ca excretion resulting from continued daily injections of salmon CT is unexplained.

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