The metabolism of creatine

Abstract

THE use of the whole animal for the study of the metabolism of creatine has a number of disadvantages. A large body of evidence exists which indicates that quite considerable quantities of creatinine may be injected into an animal, or administered parenterally, without the subsequent appearance of any extra creatine in the urine. Furthermore, the recent work of It follows that it should be possible to produce profound changes in the amounts and proportions of creatine and creatinine which are excreted by an animal merely by altering the activity of the kidney. In addition, a very large number of the known hormones is capable of influencing the excretion of one or both of creatine and creatinine, and finally, most of the possible precursors of creatine have alternative paths of metabolism, so that there is little possibility of demonstrating a quantitative conversion of precursor into creatine and thus meeting the criticism that any extra production of creatine observed may be due to a stimulant rather than to a participant action of the putative precursor. It follows that such a wealth of alternative hypotheses is available for the interpretation of the results of experimental intervention in the creatine metabolism of the whole animal that a clear-cut solution to any of the fundamental problems of creatine metabolism is hardly likely to be obtained by means of such intervention.