Effects of Insulin and Muscular Exercise upon the Uptake of Hexoses by Muscle Cells

Summary. Insulin has been found to increase the rate at which D‐galactose is lost from the extracellular space of perfused hind limb preparations of cats. Electric induction of muscle contractions in the same preparation also raised the rate of disappearance of D‐glucose and D‐galactose from the extracellular space, but had no such effect on D‐fructose. These and previous findings in this laboratory confirm those obtained by L evine , G oldstein et al. on eviscerated, nephrec‐tomized dogs and thus support the view that insulin and activation of muscle exert selective effects on the uptake of various hexoses by muscle cells. The mode of uptake of sugars by muscle cells is discussed, and it appears that it is still impossible to decide whether sugars can cross the cell boundaries in the free state or only by way of some chemical transformation. While not at all sufficient to cover the augmented metabolic rate, the rise in glucose uptake during muscular activation was still quite appreciable (viz. of the same magnitude as the rate of uptake in the resting preparation) and in the intact organism it must be met by increased glucose output from the liver. The nature of such compensatory reactions is still unknown.