Nutrient regulation of insulin-like growth factor-1

Insulin-like growth factor-I (IGF-I) is a nutrient-regulated growth factor. In malnutrition, serum IGF-I levels fall despite normal or elevated growth hormone (GH) levels and this is caused by resistance to GH, defects in IGF-I gene transcription and translation, and mRNA instability. Because IGF-I production is sensitive to protein and energy deficiencies, serum IGF-I levels may be valuable in the assessment of the nutritional status of patients with wasting diseases, including advanced renal failure. It should be recognized, however, that serum or tissue IGF-I peptide levels do not always reflect IGF-I gene expression. For example, in the K-deficient rat, kidney IGF-I levels are increased even though IGF-I mRNA levels are low. This appears to be due in part to increased sequestration by TGF-binding proteins and by decreased kidney IGF-I degradation. The increase in kidney IGF-I may contribute to the exaggerated renal growth that occurs in hypokalemia.