Organ-specific effects and interactions of acute insulin-like growth factor I (IGF-I) and growth hormone (GH)

The acute organ-specific and metabolic actions of Insulin-like Growth Factor-I (IGF-I) and Growth Hormone (GH) were investigated in normal rats. Rats received a single subcutaneous injection of IGF-I (100 micrograms), GH (100 micrograms) or a combined treatment with IGF-I (100 micrograms) plus GH (100 micrograms) following a 2(2) factorial design. The acute treatment with IGF-I produced an increase in its plasma concentration along with a reduction in insulin levels. Plasma glucose and total cholesterol decreased in all treated groups as well as triglycerides in IGF-I treated animals as compared to controls. The rates of protein synthesis, measured by amino acid incorporation were not affected by any of these treatments in muscle or liver. However, GH treatment raised the rate of protein synthesis in the jejunum, while IGF-I treatment produced an increase in tibia protein synthesis rate. Negative interactions between GH and IGF were noted concerning tibia and jejunum protein formation. Thus, GH appeared to inhibit the response to IGF-I in bone, while IGF-I inhibited the response of the jejunum to GH administration. Also, liver cathepsin activity was reduced, while bone alkaline phosphase was increased by the GH treatment. Therefore, these results have demonstrated some acute organ-specific anabolic effects and interactions of IGF-I and GH on different aspects of metabolism in normal rats.