The fate of the sugar disappearing under the action of insulin

The apparent disappearance of sugar injected into normal animals has for a long time puzzled physiological investigators (Bang, Meltzer and Kleiner, Palmer, Woodyatt). When insulin was discovered it was apparent that an agent was available by which the normal processes could be exaggerated, and therefore more easily studied. It was soon shown that the administration of sugar and insulin to the diabetic animal resulted in an increased combustion of carbohydrate and the accumulation of glycogen in the depôts. When, however, attempts were made to trace the fate of the sugar which disappears from the blood of the normal animal under the influence of an injection of insulin, difficulties were encountered. McCormick and Macleod (1) studied the effect of insulin on the glycogen reserves of rabbits which had been starved and treated with epinephrin. In some of the experiments glucose was administered subcutaneously during the period of action of insulin. No significant difference between the glycogen content of the muscles of the control animals and of those which received insulin was observed. The glycogen of the livers of the insulin-treated animals was slightly less than that of the control animals. Macleod (2) concluded from these experiments “that less glycogen is deposited both in the muscles and the liver when insulin is given along with sugar to previously starved animals than when the same amounts of sugar are given alone.” In the experiments of Dudley and Marrian (3), in which the effect of insulin on the liver glycogen of mice was studied, a much smaller amount of glycogen was found in the livers of the animals which received insulin than in those which served for controls. In another series of experiments in which insulin was administered to rabbits which had been previously fed on a carbohydrate rich diet, the glycogen content of the liver and skeletal muscles of the insulin-treated animals was again much less than that of the control animals. In both series of experiments the animals were killed after convulsions had supervened. The experiments of Babkin (4) are similar to those of McCormick and Macleod. In some of his experiments Babkin kept the blood sugar of the rabbits at a high level by the administration of sugar. He found no increase in glycogen after insulin. Kuhn and Baur (5), in a study of the effect of insulin on the glycogen content of the skeletal muscles of rabbits and guinea-pigs, found that, after insulin convulsions, the glycogen had practically disappeared from the muscles of these animals. They are undecided as to whether the depletion of glycogen is a primary effect of insulin or is to be attributed to the convulsions.