Strontium-Calcium Discrimination Factors in the Rat

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Abstract
The term "Strontium-calcium Observed Ratio" (OR) is proposed and defined to designate the over-all discrimination that occurs in movement of the 2 elements from one phase to another in a biological system. The term "Strontium-calcium Discrimination Factor" (DF) is proposed and defined to characterize the contribution of individual processes to the over-all discrimination. Double tracer studies of labeled Ca and Sr ingestion over a 20-day-period gave the same OR values as methods based on lifetime feeding. Absorption from the tract and urinary excretion were the major processes by means of which the rat discriminated against dietary strontium in favor of calcium. There is evidence of slight strontium preference in movement of the two elements from blood to bone. Excretion into the gastrointestinal tract did not contribute significantly to the over-all discrimination. Rats on a nonmilk diet (ORbone-diet = 0.27) discriminated more against strontium than did those on a milk diet (ORbone-diet = 0.57). This behavior was related to the absorptive process.