The Impact Of Growth Hormone In Muscle Morphology And Metabolism

Object: The physiological effects of GH are widely studied, esp. in clinical medicine. But the definite role of GH on the morphology and function of skeletal muscle are not well understood, esp. under the process of exercise. Skeletal muscle is an important part of kinetic system, and plays an indispensable role in maintaining the normal physical activity. We studied the effect of rhGH on the skeletal muscle morphology and metabolism function of rest and training rats. We observe the physiological role of exogenous rhGH on skeletal muscle systematically in order to make full realize of the interaction of rhGH and exercise on it.Materials and Methods:28 male mature SD rats were randomly divided into 4 groups, i.e. rest group (n=8), injection group(n=6), exercise group(n=8) , exercise plus injection group(n=6). After all the groups had been adapted for one week, the exercise group and exercise plus injection group performed closely monitored training in treadmills (grade of 5, at the speed of 20m/min, duration of 1 hour, 6 day/week) for 8 weeks. Injection protocol: After 4 weeks training, rhGH was given in a randomized, double-blinded, placebo-controlled design in injection group and exercise plus injection group. rhGH was injected subcutaneously, with the dose of 2.5-3mg/kg/day, at 8 p.m. everyday for 4 weeks. Sample collection and measurements were performed after the last injection in 12-hour fasting rats. The indexes we measure contains that the morphological observation, the cross-sectional area of the skeletal muscle, the total protein content, the IGF-I of skeletal muscle and plasma, the ATP synthase activity and the SDH synthase activity.Results:After morphological study, we found that after 4 weeks exogenous rhGH injection, skeletal muscular fiber hypertrophy was discovered through image analysis in injection group. We also found that in the dose administered, there were some morphological changes in most objects, such as cytoplasmic edema.After 8 weeks exercise, the cross-sectional areas of skeletal muscle slightly decrease, and that of the injection and exercise plus injection group increase significantly.In contrast to the rest group, the IGF-I level of skeletal muscle in the exercise and exercise plus injection group increase significantly, while that of the exercise group is much higher than the exercise plus injection group. The plasma IGF-I level also increase in injection and the exercise plus injection group.In contrast to the rest group, the muscle total protein increase 4.77%,31.13%,28.06% in exercise, injection and exercise plus injection group expectively.After 8 weeks exercise and 4 weeks injection, the ATP synthase activity increase significantly in the exercise group and the exercise plus injection group. In addition, the gastrocnemius muscle SDH synthase slightly decrease in each group.ConclusionThe endurance training of 8 weeks can exert some effect of the protein balance, the body total protein content increase.The endurance training of 8 weeks can increase the skeletal muscle IGF-I level of rest rats, indicating that the local secretion of IGF-I increase after training.In the dose administered in this study, growth hormone can induce some morphological changes such as the cytoplasmic edema.4 weeks rhGH injection can induce the hypertrophy of skeletal muscle, the cross-sectional area of the skeletal muscle increase significantly. Exogeneous GH administer can significantly increase the skeletal muscle and plasma IGF-I level.The changes of total protein content were paralleled with the skeletal muscle IGF-I level.rhGH can change the gastrocnemius muscle synthase , hence affect the skeletal muscle metabolism.