The formation of creatine from glycocyamine in the liver

The study of the precursors of creatine in animals has been beset by two difficulties principally. One has been the lack of really adequate biological material; the other, the lack of a specific, and at the same time sensitive analytical method. Experiments hitherto have consisted in attempts to change the urinary excretion of creatine and creatinine, or the creatine content of the tissues of intact animals or of isolated perfused organs. The normal, i.e. uncontrolled, fluctuations in tissue composition and urinary excretion are relatively large compared with the changes induced experimentally; it is often impossible to distinguish when experimental effects are observed, whether these have arisen from changes in the processes of excretion or synthesis; there may be variations in the water content of the tissues, thereby affecting their percentile composition; all of these have stood in the way of firm conclusions being drawn