**3. Insulin like growth factor-1 (IGF-1)**

Insulin like growth factor-1 (IGF-1), and do Mains see polypeptide targets hormone for GH. The 70 amino acids IGF-1 protein consists of 4 domain as shown in the **Figure 4**. IGF-1 mediates most of the growth-promoting actions [59]. It is synthesized in the liver and extra hepatic tissue (principally muscle, bone, and kidney). It is a 7.7 kDa single-chain polypeptide that is also found in the pituitary gland [18, 60]. IGF-1 has an A and B chain that are joined by disulfide bonds, just like insulin does. The 12 amino acids in the C-peptide region. IGF-1's ability to attach to the insulin receptor (with low affinity) is demonstrated by its comparable structure to insulin [61]. IGF-1 provides negative feedback regulation of GH production and secretion by acting at the endocrine and paracrine level. The liver, high-affinity binding proteins like IGF-binding protein 3 (IGFBP3), and transport are where about 80% of IGF1 is produced. It controls IGF1 cell-surface receptor availability to mediate IGF-1 peptide activity as well [62].

Based on the person's age, circulating IGF-1 levels change. As a result of the decreased GH levels, there is initially an uptick from birth to puberty, which is then followed by a steady decline with age [63] IGFBP1–6, a group of six IGF-binding proteins, control the bioavailability and half-life of circulating IGF-1. Each IGFBP can bind to IGF-1 with a high degree of affinity, and it is controlled by a number of particular IGFBP proteases [64]. IGF-1 is a potent inhibitor of apoptosis and has a significant impact on cell proliferation and differentiation [65]. The liver is where IGF-1 is primarily produced [66]. Age and nutrition are just two of the variables that affect serum IGF-1 levels. However, GH is the main factor controlling IGF-1 release into the bloodstream and synthesis in the liver [67].

**Figure 4.** *Structure of IGF-1 [58].*
