ABSTRACT

Insulin-like growth factor I (IGF-I) is a polypeptide hormone whose primary structure is highly homologous with proinsulin. The predominant effects of IGF-I on metabolism are to provide a signal to cells that adequate nutrition is available to avoid apoptosis, enhance cellular protein synthesis, enable cells to undergo hypertrophy in response to the appropriate stimulus, and allow cellular replication. IGF-I is a potent stimulus of protein synthesis in skeletal tissue such as muscle, bone, and cartilage. Although it stimulates protein synthesis in all cell types, these three tissues account for the bulk of the anabolic response after IGF-I administration. IGF-I concentrations are important factor in maintaining normal skeletal mass. IGF-I contributes not only to an increase in bone size but also to increased bone mineral density. The ability of IGF-I to modulate carbohydrate metabolism is consistently modified by the influence of both growth hormone and insulin.