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Effects of Dietary Calcium and Phosphorus Levels upon the Physiological Behavior of Calcium and Phosphorus in the Rat^1,2,

One Figure

University of Tennessee — Atomic Energy Commission Agricultural Research Program, Oak Ridge, Tennessee

With the use of radiochemical procedures the behavior of labeled calcium and phosphorus was studied as a function of the dietary levels of these elements. Data obtained with more than 250 growing rats indicated that:

1. Current calcium intake was of less influence upon endogenous losses than was the calcium status of the animal at the time of measurement. Endogenous fecal calcium increased from 1 to 10 mg per day for rats maintained on low- and high-calcium diets, respectively.

2. Utilization efficiency, as measured by true digestibility measurements, decreased with increased dietary calcium intake.

3. Total absorption and retention of radiocalcium were increased in rats with low calcium body stores, whereas radiophosphorus was absorbed but was subsequently re-excreted by way of the kidneys and less was retained.

4. The behavior of the Ca-45 retained by the tissues was practically independent of the dietary calcium and phosphorus levels studied, except that calcium-depleted animals demonstrated greater Ca-45 concentration and rate of turnover in all tissues.

5. Calcium maintenance requirements appeared to be a function of the animal's calcium status at the time of measurement. Animals reared to 85 days of age on rations furnished 24 and 100 mg of calcium per day required 5 and 21 mg of calcium per day, respectively, to maintain this calcium status.

6. Balance data appear to be basic for the interpretation of the behavior of Ca-45 and P-32 in the animal body. These simple procedures for estimates of endogenous calcium suggest application to studies of other factors involved in the physiological behavior of these minerals in animals.

² Radioactive isotopes were obtained from the Oak Ridge National Laboratory on allocation from the U. S. Atomic Energy Commission.

³ Present address: Animal Husbandry Department, Purdue University, Lafayette, Indiana.

Manuscript received 19 March 1954.