The creatine content of muscle under normal conditions. Its relation to the urinary creatinine

Abstract

Though an unusual amount of attention has been devoted to urinary creatinine since the introduction of Folin's simple colorimetric method for its estimation in 1904, relatively little consideration has been given to the supposedly related muscle creatine. The few figures which have been published giving the content of muscle creatine have simply served to indicate that the creatine content of vertebrate muscle is in round numbers .4 per cent., though figures for different animals have shown individual results varying from .3-.5 per cent. We have estimated the creatine concentration of muscle in a number of the common laboratory animals, rabbit, dog, cat, guinea pig, monkey, and likewise in man, in a few instances, where we have been able to obtain good samples at autopsy. Our muscle analyses on 20 normal rabbits and 5 dogs have yielded very uniform figures and indicate that the creatine concentration of rabbit muscle is .52 per cent. and of the dog muscle, .37 per cent. Our data on the muscle of the other species are as yet insufficient to warrant special comment. This uniformity recalls the constancy of the daily creatinine elimination first noted by Folin.

It is a curious fact that the creatinine coefficient of the rabbit is fully a third higher than that generally found in man and various experimental animals, dog, pig, and guinea pig. In forty rabbits, the average coefficient has been found to be 14.3 while for a healthy man, the normal coefficient is about 9, and for the dog, the average is probably a little lower (for 3 animals it was found to average 8.4). Comparing these values with those for the creatine concentration of the muscle (rabbit .52, man .39 and dog .37 per cent.), an interesting, and, as we believe, more than an accidental relationship is revealed.