Growth hormone (GH) is a peptide hormone. It stimulates growth and cell reproduction in humans and other animals. It is a 191-amino acid, single chain polypeptide hormone which is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland. Somatotrophin refers to the growth hormone produced natively in animals, the term somatropin refers to growth hormone produced by recombinant DNA technology, and is abbreviated "rhGH" in humans.

This hormone is used clinically to treat children's growth disorders and adult growth hormone deficiency. In recent years, replacement therapies with human growth hormones (HGH) have become popular in the battle against aging. Reported effects include decreased body fat, increased muscle mass, increased bone density, increased energy levels, improved skin tone and texture, and improved immune system function. At this time HGH is still considered a very complex hormone and many of its functions are still unknown.

In its role as an anabolic agent, HGH has been used by competitors in sports since the 1970s, and it has been banned by the IOC and NCAA. Traditional urine analysis could not detect doping with HGH, so the ban was unenforceable until the early 2000s, when blood tests that could distinguish between natural and artificial HGH were developed. Blood tests conducted by WADA at the 2004 Olympic Games in Athens, Greece primarily targeted HGH.

Gene locus

main: Growth hormone 2 The genes for human growth hormone, known as Myles and Growth hormone 2, are localized in the q22-24 region of chromosome 17 and are closely related to human chorionic somatomammotropin (also known as placental lactogen) genes. GH, human chorionic somatomammotropin, and prolactin (PRL) are a group of homologous hormones with growth-promoting and lactogenic activity.

Molecular structures

The major isoform of the human growth hormone is a protein of 191 amino acids and a molecular weight of 22 124 daltons. The structure includes four helices necessary for functional interaction with the GH receptor. GH is structurally and apparently evolutionarily homologous to prolactin and chorionic somatomammotropin. Despite marked structural similarities between growth hormone from different species, only human and primate growth hormones have significant effects in humans.

Regulation

Peptides released by neurosecretory nuclei of the hypothalamus (Growth hormone releasing hormone and somatostatin) into the portal venous blood surrounding the pituitary are the major controllers of GH secretion by the somatotropes. However, although the balance of these stimulating and inhibiting peptides determines GH release, this balance is affected by many physiological stimulators (e.g exercise, nutrition, sleep) and inhibitors of GH secretion (e.g. Free fatty acids).