Abstract
It is generally believed that creatine is a tissue constituent with a special function and that it arises in the body as a result of a specific cellular demand for it. There is also much evidence to show that it may also be derived from certain precursors, e. g., arginine, 1 glycine, 2 cystine, 3 and histidine, 4 in the diet.
About 3 years ago, using young rats and mice, it was observed in this laboratory that the feeding of d-arginine monohydrochloride gave slightly larger increases in muscle creatine than creatine itself, when each of these substances formed 5% of the standard casein diet. The possibility that this amino acid was one of the precursors of creatine in the animal body was suggested. With positive evidence for the other amino acids mentioned above, a systematic study was begun to determine the influence of feeding proteins, amino acids, and related substances upon creatine formation in the muscles, and creatinine elimination in the urine, the results of which are presented below.
Young rats were placed on Sherman's Diet B for a period of 10 days after weaning. Amounts of purified amino acids up to 1.5 gm. were fed either as such or mixed with a small amount of the stock diet. In other experiments casein or edestin were fed. At the end of 17 to 48 hours the animals were killed and the muscle creatine determined by the method of Rose, Helmer and Chanutin. 5 The litter mate control animals received no amino acid or protein supplement. The average creatine content of the muscles of 118 control rats was 0.40%. The average results obtained are given in Table I.
The effect of amino acid feeding upon creatinine elimination in the urine was next studied with the hope that further light might be thrown upon the origin and metabolism of creatine.
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