Variations in the Urinary Creatinine Excretion of Rats Fed Diets with Different Protein and Amino Acid Content

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Abstract
A series of experiments was carried out with adult male rats to study the effect of varying the dietary protein and amino acid content in relation to the daily creatinine excretion. It was observed that creatinine excretion was not constant and varied with protein intake and amino acid content. On the basis of these experiments, no pattern which would permit prediction of creatinine excretion as it relates to the level of dietary N or of amino acids could be distinguished. With a free amino acid-containing diet which provided the least amount of dietary N offered in these experiments, daily creatinine excretion was highest, the excretion being approximately 3 times as high as with a diet which provided 15% protein. Considerable variation in creatinine excretion of individual rats fed any given diet was observed, particularly following a change from one diet to another. The problems inherent in the use of creatinine excretion values for the calculation of body composition and other metabolic values are discussed.