Insulin growth-promoting effects

Growth promoting effects of insulin occur via interaction of the IR with Grb-2 or SHC adaptor proteins. The cascade from Grb-2 or SHC includes ras, raf, sos and MEK, culminating in activation of the gene transcription factor MAPK. Refer again to Figure 4.21. 

Since the original description of Detrisac et al. [46] a 1 1 mixture of DMEM and HAMF12, supplemented with hydrocortisone, triiodothyronine, insulin, transferrin and selenate (currently known as K1 medium) [51], has been the most widely used medium in human (proximal) tubular epithelial cell culture. Several authors add serum because of its growth promoting effect. 

GH is only one of many honnones involved in growth. Others are thyroxine, cortisol, the sex steroids, insulin, and a number of paracrine growth factors, particularly the somatomedins or insulin-like growth factors (IGFs) which mediate the growth promoting effects ol growth hormone. 

GH has been shown to have many different metabolic effects. Which of these contribute directly to its growth-promoting activity is not clear. The hormone stimulates synthesis of proteins and nucleic acids in a wide range of tissues. It has actions on carbohydrate metabolism, including both diabetogenic and insulin-like actions, and also has effects on lipid metabolism, particularly in man. Overall, GH tends to switch metabolism from utilization of carbohydrate to utilization of fat [14], although there are marked differences between species in the relative importance of actions on different aspects of metabolism. 

Insulin-like growth factors (IGFs) or somatomedins are in a family of polypeptides with growth-promoting activities and which can also modulate some of the shortterm metabolism effects of insulin [47,48]. 

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