Physiological Regulation of Insulin-Like Growth Factor Expression
The insulin-like growth factors (IGF) I and II comprise a structurally homologous pair of circulating polypeptides of fundamental importance in mammalian growth processes (1). Although IGF-I is a major mediator of growth hormone (GH) action and is predominantly expressed during postnatal life, while IGF-II is synthesized primarily during fetal development (1,2), the precise roles of either peptide in promoting tissue growth remain at best incompletely understood. In addition the relative contributions of circulating versus locally-produced IGFs toward organ or tissue growth also are unknown. With the advent of cloned probes for mammalian IGF genes (3–8) it has become possible to more accurately assess the biosynthesis of IGFs I and II in various tissues and thus potentially to determine the roles of these growth factors as paracrine, autocrine or endocrine agents. Summarized in this chapter are results of several experiments designed to analyze the mechanisms involved in the control of IGF synthesis in vivo. Our data indicate that during growth of skeletal muscle both systemic and local factors can regulate the production of mRNAs for IGFs I and II. In the kidney peripheral GH administration stimulates IGF-I mRNA in collecting duct cells, with a consequent increase in IGF-I.
KeywordsSatellite Cell Growth Hormone Treatment Plantaris Muscle Unilateral Nephrectomy Renal Hypertrophy
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