[Importance of the thyroid gland in calcemic homeostasis during intestinal calcium absorption in man]

The importance of calcitonin (CT) in calcaemic homeostasis has been studied in control subjects and in thyroidectomized patients. After administration per os of a calcium load together with a radioactive tracer, calcaemia increases more markedly in thyroidectomized cases while the radioactivity curve shows no difference between the two groups. Unlike the controls, in patients the absorption-induced calcaemic increment curve coincided with the cumulative intestinal calcium absorption curve evaluated by the biradioisotopic method. Thus absorption-induced hypercalcaemia in athyroid subjects would not seem to be controlled by homeostatic factors. Through CT, the thyroid exerts an evident, though limited, braking action on calcaemic increase due to absorption. Considering that absorption of calcium is prolonged for a number of hours, CT secretion will last at least as long as will its action on the skeleton. The saving of skeletal mineral that follows may be considered to be physiologically more important than the effect of the hormone on calcaemic homeostasis.