Physiological characteristics of the somatotropin-insulin-like growth factors axis in calves during the foetal and postnatal development
2010
Georgiev, I., Thracian University, Stara Zagora (Bulgaria)
The purpose of this review was to summarize and analyze the available information about some physiological traits of insulin-like growth factors and their cell receptors. Insulin-like growth factors - IGF-1 and IGF-2 are single-chain low molecular polypeptides with structure similar to that of proinsulin, exhibiting a very broad spectrum of physiological activity. IGF-1 and IGF-2 are formed in the liver as well as locally in almost all tissues. Due to the variety of physiological effects of IGFs and the fact that their production is stimulated by somatotropin, the term growth hormone-insulin-like growth factors axis - GH-IGFs is commonly accepted. Apart IGF-1 and IGF-2, this system also includes insulin, somatotropin, four tissue receptor types – insulin receptor - IR, insulin like growth factor 1 and 2 receptors - IGF-1R and IGF-2R, growth hormone receptor - GHR, 6 IGF binding proteins - IGF-BP-1, IGF-BP-2, IGF-BP-3, IGF-BP4, IGF-BP5 and IGF-BP6. Despite the unclear facts related to the physiological traits of the different factors of the GH-IGFs system in animals, it is believed that they are essential for regulation of tissue growth and development via its effects on cell proliferation and differentiation and that their importance for these events changes during the foetal and postnatal periods.
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