Some findings on the mechanism of adaptation of the intestine to calcium deficiency

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Abstract
I. The rate of absorption of calcium was measured in vivo by an isotope technique in rats given either a normal or a low-Ca diet. 2. Increasing the amount of Ca injected into the lumen of the intestine decreased the rate of Ca absorption. When the dose was greater than 100-150 pg Ca the degree of absorption was a linear function of the Ca concentration in both duodenum and jejunum. 3. In rats given a Ca-deficient diet for z weeks the absorptive capacity of both the duodenum and jejunum was significantly enhanced. Judged by the changes in the rate of absorption with different doses, some saturahlc mechanism seemed to be involved in this phenomenon. 4. Parathyroidectomy before adaptation to Ca deficiency prevented the increase in Ca absorption in Ca-deficient rats but diminished it only slightly in rats given a normal diet. Parathyroidectomy performed after the development of adaptation to Ca deficiency also decreased Ca transport across the intestine, which suggests that the parathyroids are necessary for increasing the capacity of the rat intestine to absorb Ca.

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