Effect of Inslulin Administration on the Physical Performance of Rats and Mice

ABSTRACT

The correlation between muscle glycogen content and physical performance in mice was evaluated by investigating whether an increase in glycogen content in skeletal muscle with insulin administration can improve the physical performance without other effects of exercise. Albino rats(group I) were divided into two groups, i.e., insulin and saline administered group. The former experimental group was treated with protamine zinc insulin(15U/kg/day) subcutaneously for two weeks to increase the content of the muscle glycogen and the latter control group with saline. Mice (group II) were also divided into insulin treated and control groups and both groups were subjected to running exercise on an animal treadmill up to point of exhaustion once every day. After two weeks of insulin treatment, the muscle glycogen content, the maximal running time and the maximal swimming time were measured in non-exercised group I. In group II, after 12 days of insulin and saline administration, the muscle glycogen content, the maximal running time, concentrations of lactate and pyruvate in the blood were measured before and after the maximal exhaustive running. The results were summarized as follows. In group I, the muscle glycogen content, the maximal running time and the maximal swimming time of the insulin administered group were significantly greater of the control groups. In group II, the maximal running time was significantly greater(P < 0.01) in the experimental group than of the control group, while the muscle glycogen content revealed no significant difference between the two groups. On the other hand, lactate concentration and lactate/pyruvate ratios in the blood were significantly lower in the experimental group than those of the control groups. From the above results, it may be concluded that the elevation of muscle glycogen content alone by insulin treatment without any previous physical training can improve physical performance of rats. And insulin was also found to improve physical performance even in experimental animals which had been subjected to a longterm of exercise.