Glucose infusion attenuates fatigue without sparing glycogen in rat soleus muscle during prolonged electrical stimulation in situ

Abstract

Carbohydrate administration increases endurance in man, and this could be associated with a reduction in muscle glycogen utilization in type I but not in type II fibres. Glucose infusion also attenuates fatigue in the rat plantaris muscle (94% type II fibres) stimulated indirectly in situ, but this is not associated with a glycogen sparing effect. The aims of this study were to verify if glucose infusion would attenuate fatigue and would reduce glycogen utilization in a muscle predominantly composed of type I fibres. For this purpose, the soleus muscle (84% type I fibres) was indirectly stimulated in situ in anaesthetized rats for 60 min while infusing either saline or glucose (1 g.kg⁻¹.h⁻¹; plasma glucose 7.7 mmol.l⁻¹ vs. ~5 mmol.l⁻¹ with saline only). The experimental data were expressed as the means (SD). With and without glucose, the dynamic force decreased by ~20% in the first minute of stimulation. With the infusion of saline, the dynamic force further decreased to 55% of the initial value at the end of the 60-min period of stimulation, but when glucose was infused for 60 min, the dynamic force remained constant at 78% of the initial value. When glucose was infused starting at min 30, dynamic force was partially restored. However, muscle glycogen utilization was not significantly different with the infusion of glucose compared to with the infusion of saline. These results suggest that glucose infusion attenuates fatigue in type I muscle fibres, but that this is not associated with any muscle glycogen sparing.