THE COPARATIVE STUDY OF MECHANISM OF INSULIN ACTION ON MUSCLE CARBOHYDRATE METABOLISM

Abstract The results of three series of experiments are presented in the paper. In the first one the action of three different insulins - the mammalian (porcine), the avian (chicken) and the fish (scorpionfish) on the same muscle, i.e. the isolated rat diaphragm, was investigated. The enhancement of glucose uptake served as an index of muscle response to the applied dose of insulin. The experiments showed that the responses of the muscle to mammalian and avian insulins were similar with all the investigated concentrations of the hormone. But in the case of fish insulin the dose-effect curve was quite different: the threshold dose was about 100 times greater than in the case of the porcine hormone; the curve rose abruptly and reached the maximal height with the same concentration as in the case of mammalian and avian insulins. The study of the binding of insulins by the diaphragm led to the conclusion that the peculiar character of the effect of fish insulin on glucose uptake was due to the inability of mammalian muscle receptors to interact adequately with the fish insulin. In the second series of experiments the response of various muscles (mammalian, avian, fish cyclostomean and acranian) on the same insulin, namely the porcine was studied. The following indices of insulin action were used: the enhancement of glucose uptake, the rise of glycogen content, the activation of glycogen synthetase and the increase of the permeability of the muscle to D-xylose or L-arabinose and consequently to glucose. The experiments indicated that insulin exerts basically the same effects on muscle carbohydrate metabolism at all stages of evolution of the chordata. It stimulates the glucose uptake by the muscle; the effect being due to two mechanisms: the enhanced transport of glucose into the cell and augmented synthesis of glycogen. As a rule, insulin triggers the action of both mechanisms, but they are not interdependent, and in some natural or experimental conditions one of the mechanisms may not take place. The experiments of the third series showed the isolated muscles of the scorpionfish to be more sensitive to the fish insulin than to the mammalian one. As it was stated above, the isolated rat diaphragm is much more sensitive to the mammalian insulin. The chicken muscles would rather respond to the mammalian insulin than to the fish one. As far as muscles of lampreys and lancelets are concerned, they do not discriminate between the insulins used.