**2. Growth hormone and insulin-like growth factor 1**

GH and IGF-1 are key links in the neurohumoral regulation of overall metabolism and can act through various intracellular signaling pathways. GH stimulates IGF-1 synthesis, which, in turn, affects GH production by the principle of negative feedback, inhibiting its synthesis (**Figure 1**).

The physiological effects of GH and IGF-1 on cells are mediated through transmembrane receptors found on the surface of many cell types, including hepatocytes and lymphocytes [10]. The effect of GH and IGF-1 is largely determined by the level of receptor expression, which depends on cell type and can change under the influence of various factors. The action of the GH/IGF-1 axis depends on GH and IGF-1 production on one hand, and IGF-binding proteins, proteases that degrade the IGFbinding proteins complex, and GH and IGF-1 receptors, on the other hand [11].

GH is synthesized in the anterior pituitary cells and secreted into the blood, with peak blood levels every 3–5 hours. The highest blood content of the hormone occurs during fetal development. With age, the baseline, frequency, and amplitude of hormone secretion peaks decrease. The nature of GH secretion differs in men and women and depends on age. The range of baseline GH levels in children aged 1–3 years is 2–10 ng/m, in adults, 1–5 ng/ml [12, 13].

IGF-1 is a polypeptide hormone produced by many tissues, but more than 90% of circulating IGF-1 is synthesized by hepatocytes [3]. Serum IGF-1 levels, in contrast to GH, practically do not change during a day. The range of reference IGF-1 levels in children aged 1–3 years is 5–300 ng/ml; the maximum IGF-1 level in children is observed during puberty and gradually decreases with the years [14, 15].

Growth regulation is one of the main functions that GH and IGF-1 have in common. In addition, GH in both children and adults plays an important role in the regulation of metabolism. IGF-1, being a major mediator of anabolic and mitogenic effects of *Growth Hormone and Insulin-like Growth Factor-1 in Children with Cholestatic Diseases… DOI: http://dx.doi.org/10.5772/intechopen.108301*

#### **Figure 1.**

*Scheme of neurohumoral regulation of growth by the GH/IGF-1 system. GHRF – growth hormone releasing factor, GH – growth hormone, GHR - growth hormone receptor, IGF-1 – insulin-like growth factor 1, IGFBP – IGF binding protein, IGFR – IGF receptor.*

GH in peripheral tissues, is an important factor in body mass regulation. However, GH and IGF-1 have different effects on glucose and lipid metabolism: GH increases blood glucose levels and promotes lipolysis, whereas IGF-1 has opposite effects [16–18].
