The presence of creatinine in muscle

Abstract

The presence of creatinine in muscle has, in general, been denied by those who have undertaken a study of this question. In earlier communications 2 upon various phases of the creatine-creatinine problem, evidence has been presented which is strongly in harmony with the metabolic relationship of these two substances. Since creatinine is so rapidly eliminated from the body, its presence in the muscle tissue would not be expected in large quantity. On the other hand, if creatinine originates from creatine, this transformation might be expected to take place in the muscle tissue, and on this account it would seem that, with sufficiently delicate and reliable methods, it ought to be possible to detect the presence of creatinine. We believe we have demonstrated that creatinine does exist in very small quantity in muscle (rabbit), equivalent to about one per cent. of the creatine. The quantity appears to average 6 or 7 mgm. per 100 grams of moist muscle, although variations of 3 to 10 mgm. have been encountered. An observation which is much more significant, however, is that, when the muscle is allowed to autolyze at body temperature under antiseptic conditions, the creatinine content increases at a very uniform rate at the expense of the muscle creatine. One experiment may be cited. The muscle of Rabbit No. 77 had an initial creatinine content of 6 mgm. per 100 grams; at the end of 2 days this had increased to 20.2 mgm., in 4 days to 36.6 mgm., in 6 days to 50.6 mgm., in 8 days to 62.5 mgm., and in 10 days to 74.5 mgm., an average uniform daily increment of 7 mgm. per day. This fact, when considered in connection with the uniform content of muscle creatine previously observed by us, 1 is, we believe, the fundamental factor in bringing about the constant daily excretion of creatinine originally observed by Folin.