Creatine metabolism in skeletal muscle of cold-acclimated rats

Creatine metabolism in skeletal muscle of cold-acclimated rats was studied with the aid of [14C]creatine as a tracer. Creatine contents of all muscles studied were significantly lower in cold-acclimated rats than in controls. Radioactive creatine uptake by soleus of cold-acclimated rats was significantly lower than that of controls, while radioactive creatine uptakes by heart, diaphragm, and gastrocnemius of cold-acclimated rats were not different from those of controls. Urinary creatine dervied from muscle creatine plus urinary creatinine, which corresponds to total creatine release from muscle, increased in the early stage of cold exposure and was restored to control level after completion of cold acclimation. Creatine turnover rate in skeletal muscle was not different between control and cold-acclimated rats. These findings indicate that cold acclimation results in reduced creatine content and uptake of skeletal muscle, and could be interpreted as reflecting enhanced ability of nonshivering thermogenesis in skeletal muscle.