Effect of hyperglycaemia on muscle glycogen mobilization during muscle contractions in the rat

In the rat, muscle glycogen is mobilized during the first stage of exercise, despite normoglycaemia. The aim of the present study was to examine if this process could be prevented or reduced by hyperglycaemia. Three experiments were carried out: in the first, rats were forced to run on a treadmill; in the second the gastrocnemius muscle group was made to contract by stimulation of the sciatic nerve and in the third adrenaline was administered subcutaneously. Each group was divided into two subgroups: control and enriched with glucose (hyperglycaemic). It was shown that hyperglycaemia has no effect on running-induced glycogen mobilization in hind-limb muscles of different fibre composition but prevented it totally in diaphragm muscle. Hyperglycaemia also did not affect the glycogen mobilization induced by stimulation of the sciatic nerve. However, it delayed and reduced markedly the glycogenolytic effect of adrenaline. It is concluded that increased glycogenolysis in muscles at the beginning of exercise may be a consequence of a delay in the activation of glucose transporting mechanisms in muscle cells.