Effect of insulin on the uptake of creatine-1-14C by skeletal muscle in normal and x-irradiated rats

The uptake of labeled creatine by skeletal muscle was enhanced in rats treated with 2 units of NPH insulin on each of two successive days and then injected ip with creatine-1-14C. While the uptake of labeled creatine by muscle was impaired in rats exposed to an X-ray dose of 500 rads, this impairment was relieved by treatment with insulin after X-irradiation. The level of radioactivity and the creatine concentration in whole blood was lower in insulin-treated rats injected ip with creatine-1-14C than in untreated controls. In contrast, X-irradiated rats injected ip with labeled creatine exhibited higher levels of radioactivity and a higher creatine concentration in blood than did the sham-irradiated controls. When X-irradiated rats were treated with insulin, the amount of radioactivity and the creatine concentration in the blood 1 hr after the injection of labeled creatine was not significantly different from that in the sham-irradiated controls. These observations are consistent with the view that insulin enhances the transfer of creatine from the circulation into skeletal muscle in normal as well as in X-irradiated rats.