Further studies on muscle creatine

Abstract

In an earlier communication, 1 attention was called to the constancy in the content of muscle creatine for normal animals of a given species, though distinctive for different animals. It was further pointed out that during starvation in the rabbit, the percentage content of muscle creatine may show either an increase or a decrease, the latter depending in considerable part upon the rate and amount of creatine eliminated in the urine.

These observations have been extended to rabbits which have been fed for varying periods upon carbohydrate—without fat or protein. Carbohydrate feeding greatly reduces the elimination of creatine in the urine, as previously observed, though the creatine content of the muscle does not materially differ from that found during a similar length of starvation. In other words, it may be markedly decreased during a long period of carbohydrate feeding. It seems probable that the action of the carbohydrate is simply one phase of the sparing action of carbohydrate on protein metabolism, in this case allowing sufficient time for the body to handle the creatine, i. e., to oxidize it, or change it to creatinine.

That creatine when fed or injected does not reappear in the urine in the form of creatinine, except in traces, or in large amount unchanged, unless given in considerable quantity, has been as-certained by a number of investigators. The possibility that this creatine, which remains unaccounted for, is stored up in the muscle has not been adequately studied.

has not been adequately studied. In four experiments on rabbits, the creatine content of the muscle, after repeated subcutaneous injections of creatine, has been found to be uniformly slightly above (4-7 per cent.) the normal amount. This would appear to indicate that a small atnount of the injected creatine was deposited in the muscles, though insufficient to account for the creatine not eliminated in the urine either unchanged or in the form of creatinine.