The influence of insulin on carbohydrate metabolism in the isolated diaphragm muscle of normal and alloxan diabetic rats

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Abstract
The fate of uniformly labelled 14 C glucose in the isolated diaphragm muscle of normal and alloxan diabetic rats has been studied by a quantitative application of the radio paper-chromatographic technique. No significant differences were observed in the metabolism of glucose by muscle from normal and diabetic rats. About 80% of the glucose metabolized by the muscle in the absence and presence of insulin has been accounted for. The extra glucose disappearing from the incubation medium in the presence of insulin was found to be incorporated in oligo- and polysaccharides, the percentage of glucose converted into the other main metabolites (i.e. lactic acid, hexose-phosphate esters and CO 2 ) was shown to be unchanged or decreased by insulin. Insulin markedly accelerated the synthesis of oligo- and polysaccharides. The amount of free glucose in the tissues, which reached a maximum after 15 min of incubation, was uninfluenced by insulin. When the muscle was first incubated with 14 C glucose and then in the absence of substrate, there was a sharp decrease in the radioactivity of all the intermediates with the exception of the hexose-phosphate esters which were found to accumulate. Under anaerobic conditions the total glucose metabolism was very reduced, and the greater part of the glucose disappearing from the medium was recovered as free glucose in the tissues. Very little radioactive lactic acid was formed under anaerobic conditions, except when the muscle was first incubated with 14 C glucose aerobically and then anaerobically; under these conditions there was a considerable accumulation of radioactive lactic acid. Current theories on the mode of action of insulin have been discussed in reference to the findings reported in the present work.

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