Modulation of the insulin-like growth factor system by chronic alcohol feeding

Insulin-like growth factor (IGF)-I is a potent anabolic agent that plays an important role in regulating muscle protein balance. Alterations in one or more of the various components of the IGF system may be in part responsible for the muscle wasting that accompanies chronic alcohol consumption. The purpose of the present study was to characterize changes in the growth hormone-IGF axis produced by chronic alcohol consumption in rats. After 8 weeks of alcohol feeding, the IGF-I concentration was decreased in plasma (31%) as well as in the liver and skeletal muscle (40-50%), compared with pair-fed control animals. In addition, alcohol consumption decreased IGF-I mRNA abundance in liver and muscle (~50%). IGF-I content in duodenum end kidney, however, was not altered by alcohol feeding. Concomitantly, the relative concentration of IGF binding protein (IGFBP)-1 was increased in plasma, liver, end muscle of alcohol-fed rats, compared with control values. In contrast, no changes in the plasma concentrations of IGFBP-2, -3, or -4 were detected in alcohol-fed rats at this time point. Previous studies have indicated that elevations in glucocorticoids or decreases in insulin or growth hormone might be responsible for the decrease in IGF-I and/or the increase in IGFBP-1 in other catabolic conditions. However, there was no difference in the plasma concentrations of these hormones between alcohol- fed and control animals in this study. These data indicate that chronic alcohol feeding in rats decreases IGF-I and increases IGFBP-1 in the circulation end in skeletal muscle and that these changes appear to be independent of changes in classical hormonal regulators of the IGF system. The observed alterations in the IGF system are consistent with a reduction in the anabolic actions of IGF-I induced by chronic alcohol consumption.