Specific decrease in liver insulin-like growth factor-I and brain insulin-like growth factor-II gene expression in energy-restricted rats.

Four-week-old male rats were maintained for 10 d on a series of diets containing a constant high level of dietary protein and total energy at 100, 70, 60 or 50% of the ad libitum intake rate. Under these conditions, growth rate varied as a function of dietary energy. Serum insulin-like growth factor (IGF)-I was decreased in the energy-restricted animals. Total hepatic IGF-I mRNA was decreased by approximately the same factor as circulating IGF-I protein. In contrast to previous results obtained with protein-restricted animals, serum albumin mRNA was not decreased in the energy-restricted animals. Brain IGF-II mRNA was slightly decreased in animals fed the 70 and 60% energy diets and was decreased by 50% in animals fed the 50% energy diet. Insulin-like growth factor binding protein-2 (IGFBP-2) gene expression was increased in the liver but not in the brain of the energy-restricted animals, indicating that dietary energy regulates IGFBP-2 gene expression differently in liver and brain. The results demonstrate specific changes in liver IGF-I and IGFBP-2 gene expression and brain IGF-II gene expression in animals that are growth-retarded because of a restriction of dietary energy.