[Studies on the creatine metabolism in cold acclimation (author's transl)]

Abstract

Creatine metabolism in cold-acclimated rats was studied with the aid of [1-14C] creatine as a tracer. Urinary creatine derived from muscle increased in the early stage of cold exposure, and creatine contents of all muscles studied were significantly lower in cold-acclimated rats than in controls. Increased urinary creatine derived from muscle and reduced creatine contents of all muscles were also observed in thyroid hormone, triiodothyronine (T3)-treated rats, while chronic treatment of noradrenaline did not affect urinary creatine derived from muscle and creatine contents of all muscles. Radioactive creatine uptake by skeletal muscle was significantly lower in cold-acclimated rats than in controls, while radioactive creatine uptake by heart and diaphragm of cold-acclimated rats was not different from that of controls. Chronic treatment of noradrenaline produced a similar change in radioactive creatine uptake by skeletal muscle, while the inhibitory effect of T3 on radioactive creatine uptake is not different among the different types of muscle, although the uptakes of radioactive creatine by all muscles studied were lower in T3-treated rats than in controls. These findings indicate that cold acclimation results in reduced creatine contents in all muscles and reduced uptake of creatine in skeletal muscle, possibly reflecting an enhanced ability of nonshivering thermogenesis in skeletal muscle induced by both thyroid hormones and noradrenaline.