The effect of growth hormone (GH) administration on insulin-resistance has frequently reported. The study-I investigated the effect of GH administration on body composition and insulin resistance in rats. Twenty rats were weight-matched and assigned ...
The effect of growth hormone (GH) administration on insulin-resistance has frequently reported. The study-I investigated the effect of GH administration on body composition and insulin resistance in rats. Twenty rats were weight-matched and assigned to following 2 groups; CON, GH groups. After 4 weeks of GH injections (0.4 IU/kg/day, 6 days/week), the plasma lipids profiles, triglyceride contents in muscle & liver, muscle glucose transport rates, OGTT, and body composition were measured in these rats. The glucose analogues 3-O-methyl-D-glucose (3-MG) have been used to study skeletal muscle (epitrochlearis) glucose transport. Epitrochlearis muscles were composed primarily of type II fibers.
After 4-week of GH administration, Insulin-stimulated (1,000 μIU/㎖) 3-MG uptake in split soleus was smaller than saline-injected control rats (1.89±0.27 vs 1.37±0.18*. *;significantly different from CON). The plasma FFA and TG concentrations in muscle & liver were significantly increased after GH administration (FFA: 0.58±0.05 vs 0.83±0.07*, TG in muscle: 0.71±0.12 vs 1.46±0.15* , TG in liver: 4.41±1.08 vs 8.77±1.37*. *;significantly different from CON), but GH injection did not significantly affect %body fat, plasma TC, TG, HDL-C concentrations. GH administration elevated the curves of the oral glucose tolerance test and insulin response compared with those of CON. Our results indicated that 4 weeks of GH administration have severe state of insulin resistance in glucose transport, but did not affect the body composition.
The study-II investigated the effects of endurance exercise on hGH-induced insulin resistance of skeletal muscle in rats. Forty rats were randomly divided into 4 groups: CON (saline injection group, n=10), GH (hGH injection group, n=10), Ex (Exercise group, n=10), GH/Ex (Growth hormone administration/ Exercise group, n=10). GH, GH/Ex animals received hGH by subcutaneous injections (0.4 IU/kg/day, 6 days/week) for 8 weeks and CON, Ex animals received saline injections with the same volume as GH. The exercise regimen was designed in a 8% grade treadmill, 24m/min training speed with 5 times/week. After 8 weeks of treatment, the plasma lipids profiles, triglyceride contents in muscle & liver, muscle glucose transport rates, OGTT, body composition, and citrate synthase activities were measured in these rats. After 8-week treatment, plasma Insulin & glucose levels in GH were significantly increased than other 3 groups during OGTT. The rate of glucose transport under submaximal insulin concentrations was significantly lower in GH being 1.02 ±0.10 μmol/ml/hr as opposed to 1.42±0.12 μmol/ml/hr for the CON. However, there was not a significant difference between GH/Ex (1.31±0.10 μmol/ml/hr) and CON. Plasma FFA levels were significantly higher in GH (0.40±0.04 mmol/ℓ), GH/Ex (0.42±0.05 mmol/ℓ) than CON (0.29±0.03 mmol/ℓ). Triglyceride contents in plantaris muscle was significantly greater in GH (0.52±0.06 μmol/g) than CON (0.36±0.01 μmol/g), Ex (0.39±0.02 μmol/g), Plasma leptin levels was significantly lower in Ex (1.45±0.22 ng/ml), GH/Ex (1.20±0.15 ng/ml) than CON (4.11±0.75 ng/ml), GH (3.62±0.49 ng/ml). Citrate Synthase Activities was significantly higher in EX (65.58±3.16 μmol/min/gww), GH/Ex (63.45±2.22 μmol/min/gww) than CON (52.39±2.16 μmol/min/gww), GH (48.15±1.48 μmol/min/gww). However GH injection did not significantly affect %body fat, plasma TC, HDL-C concentrations. In conclusion, Regular exercise training prevents GH-induced insulin resistance in rats.