Regulation of somatomedin production by growth hormone

GH also stimulates somatomedin C levels in a variety of other species, including mouse [57], sheep [58] and man [59]. In man and other species shortage of GH due to pituitary deficiency leads to lowered somatomedin C levels, and enhanced GH levels found in giantism or acromegaly are associated with elevated levels of somatomedin C. 

Actions of GH on somatomedin C production in vitro have also been demonstrated, using various different tissues. Thus the hormone has been shown to stimulate somatomedin C production by perfused rat liver [16], cultured rat hepatocytes [60,61], human fibroblasts [62] and human lymphoid cells [63] in vitro. 

There is thus ample evidence supporting the idea that GH regulates somatomedin C levels. In many respects it appears to be the major factor affecting these levels, but it should be stressed that other hormones (including thyroxine and insulin) and nutritional factors are also of considerable importance. The effects of GH on IGF-II levels are less important than those on somatomedin C placental lactogen may be more important here, in partial accordance with the idea that IGF-II is concerned particularly with the regulation of growth of fetal tissues. 

GH may also stimulate production of at least some of the somatomedin-binding proteins. Production of binding proteins by hepatocytes in vitro has been demonstrated [60,61,64], as has its stimulation by GH. The 150K binding protein appears to be controlled by GH but not the 50K protein. 

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