| Biochemical actions of GH
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| Binding of GH to its receptor precipitates a complex series of intracellular events that lead to the transcription of many enzymes, hormones and growth factors, including IGF-I
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| Figure 37.13 Biochemical functions of GH. These can be divided conveniently into direct actions on lipid and carbohydrate metabolism and indirect actions on protein synthesis and cell proliferation. |
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The diversity of action of GH makes it difficult to under-stand or integrate all of its functions; thus it is convenient to think in two distinct phases (Fig. 37.13). The direct actions of GH are on lipid, carbohydrate, and protein metabolism. During hypoglycemia, GH stimulates lipolysis and induces peripheral resistance to insulin. These effects stimulate the use of fatty acids in peripheral tissues, sparing glucose for use in the brain. Previously, GH therapy was used only for treatment of GH-deficiency in children in order to stimulate
growth; however treatment is now often extended into adulthood because untreated individuals are susceptible to hypoglycemia. This change in treatment strategy illustrates the complex effects of GH on metabolism. During growth, GH stimulates the uptake of amino acids and their incorporation into protein, especially in muscle. The indirect actions of GH are mediated by IGF-I. These actions promote the proliferation of chondrocytes and the synthesis of cartilage matrix in skeletal tissues. Although GH is most often associated with its role in stimulating linear growth, it clearly has other roles in influencing the relative amount and distribution of fat and muscle tissue.
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