The Effects of Growth Hormone Administration and Endurance Exercise Training on Insulin Resistance in Sprague-Dawley Rat

Abstract

This study 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, muscle glucose transport rates, and OGTT 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 (1000 uU/ml) was significantly lower in GH being 1.02±0.10 mol/ml/hr as opposed to 1.42±0.12 mol/ml/hr for the CON. However, there was not a significant difference between GH/Ex (1.31±0.10 mol/ 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 mol/g) than CON (0.36±0.01 mol/g), Ex (0.39±0.02 mol/g), However GH injection did not significantly affect plasma TC, HDL-C concentrations. In conclusion, regular exercise training attenuates GH-induced insulin resistance in skeletal muscle of rats.