Alterations in Dynamics of Calcium Metabolism by Intraintestinal Calcium Reservoirs

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Abstract
In a series of rabbits the continuous oral ingestion of spinach for 7 or 18 days increased the blood disappearance rate of Ca and the fecal excretion rate as measured by Ca45. Following the spinach diet the bone uptake of radiocalcium was depressed for a period up to 5 days, and urinary excretion for the next 3 days. Blood disappearance rates of Ca45 and the fecal rate of Ca excretion were increased by administering by stomach tube 1250-3750 mg. of Na versene or 20 g. of Ca dibasic phosphate. Bone uptake and urinary excretion were not significantly affected by such a single oral admin. Apparently the continuous presence of the versene or dibasic Ca phosphate through daily feeding is required. The oxalic acid of spinach, the Na versene, which complexes Ca in non-ionizable form, and large amounts of Ca dibasic phosphate, which is relatively insoluble, exert their effects by establishing a non-absorbable Ca reservoir in the intestinal tract which competes by exchange across the intestinal membrane for the Ca ions in the blood, thereby lowering urinary excretion and bone uptake. Citric acid administered orally exerted a similar effect. When radioactive Ca as CaCl2 is injected directly into the duodenum through an abdominal incision the Ca level in the blood reaches its peak in about 20 min. Thereafter the disappearance rates in the blood are similar to that for intraven. injected Ca 45. The blood values remain higher following intestinal absorption since the max. concn. in the blood reached by intraven. injn. is never achieved by the intestinal route.

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