Studies on the relationship between creatine and creatinine

When muscle tissue is allowed to autolyze, creatine is transformed to creatinine at a constant rate. The velocity of this reaction increases with a rise in temperature, although practically negligible at 0° C. The rate of formation at body temperature is nearly sufficient to account for the daily elimination of creatinine. The velocity of the reaction is increased by acids but not reduced by Henderson's neutral phosphate mixture. Added creatine experiences the same fate as the creatine originally present, while added creatinine inhibits the reaction, or if added in sufficient quantity causes it to proceed in the opposite direction. Pure solutions of creatine and creatinine experience the same transformations, although much more slowly. On the long standing of pure solutions there seems to be a slight loss in total creatinine (from both creatine and creatinine). This appears to be due in part to a transformation to urea. Whether or not these phenomena are vital factors in the formation of creatinine in the body, we are unprepared to say. To obtain further light on this point, experiments have been conducted on nephrectomized animals. The creatine and creatinine content of the various body tissues have been determined several days after a double nephrectomy. In certain of these experiments creatine and creatinine have been injected. Some what similar deductions may be drawn from our experiments in vivo to those in vitro; although there are certain differences between the two types of experiments, the significances of which are not as yet entirely clear to us.