Why the study?
Does regular exercise training prevent growth hormone-induced insulin resistance and alter muscle GLUT4 protein expression in rats?
Does regular exercise training prevent growth hormone-induced insulin resistance and alter muscle GLUT4 protein expression in rats?
Regular exercise training prevents the insulin-resistance side effect induced by growth hormone administration in rats while preserving exercise-induced increases in muscle GLUT4 and glycogen.
The insulin-resistance effect of growth hormone (GH) administration has been frequently reported. The present study investigated the effect of GH administration on glucose tolerance and muscle GLUT4 protein expression in exercise-trained and untrained rats. Forty-eight rats were weight-matched and assigned to the following 4 groups: control, GH, exercise training, and exercise training + GH groups. After 2 weeks of GH injections (65 microg/kg/day) and exercise training, the glucose tolerance and insulin response were measured in these rats. The GLUT4 protein level, glycogen storage, and citrate synthase activity were determined in red gastrocnemius and plantaris muscles. Daily GH administration elevated the curves of the oral glucose tolerance test and insulin response compared with those of saline-injected control rats. Furthermore, exercise training completely eliminated this GH-induced insulin resistance as determined 18 h after the last bout of exercise training. Additionally, exercise training significantly increased muscle glycogen storage and GLUT4 protein levels. GH administration did not affect the GLUT4 protein and glycogen storage increases induced by exercise training, but the citrate synthase activity in the plantaris muscle was further elevated by GH administration to a level above that induced by training. In conclusion, this is the first study that demonstrates that regular exercise training prevents GH-induced insulin-resistance side effect in rats.
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Yuncheng Xiao (2026) studied Growth hormone-induced insulin resistance in rats (n=48). Growth hormone administration and exercise training vs. Saline-injected untrained control group was evaluated on Oral glucose tolerance test, insulin response, and muscle GLUT4 protein expression.
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