Somatotropin, also known as growth hormone (GH), is produced by the pituitary gland and regulates growth in young animals and humans. It stimulates cells and increases protein production for cell growth. GH targets liver cells to secrete insulin-like growth factor 1 (IGF-1), which promotes bone growth. GH concentration decreases with age, but it has effects on adult metabolism. The hypothalamus secretes growth hormone releasing hormone (SRH) to increase GH production. Synthetic somatotropin, or human growth hormone (HGH), is used by athletes to enhance performance and by doctors to treat growth deficiencies.
Somatotropin is a protein-based peptide hormone that is secreted by the pituitary gland and is responsible for the growth of young animals into their adult size. In humans, it mediates the growth of children to their adult height and stimulates cells in many tissues. Also called growth hormone (GH), it has also been used by athletes since at least the 1970s to increase muscle mass and speed recovery from injuries, and has been promoted as an anti-aging drug.
GH causes genes in the nucleus of its target cells to increase the production of proteins needed for cell growth. All hormones work by binding to a receptor on the surface of their target cells, thereby changing the activity of genes in that cell’s nucleus. Most cells in the body will respond to circulating somatotropin, but there are specific targets it regulates to induce growth. Chief among these are the liver cells that secrete insulin-like growth factor 1 (IGF-1). This compound is responsible for the effects of somatotropin that characterize the growth of children, such as increased height.
When IGF-1 binds to cartilage cells, they differentiate to form new bone. The higher the concentration of these hormones, the more bone mass increases. So the highest levels of both growth hormone and IGF-1 in the human body are reached during the growth spurt of puberty, when a lot of new bone is being produced. Over a lifetime, GH concentration gradually decreases, and healthy adults will have levels less than two-thirds of those found in a young adolescent. Growth hormone has many effects on normal adult metabolism and include promoting fat metabolism, new protein synthesis, and glucose production in the liver.
Somatotropin is secreted by the anterior pituitary gland, where it is produced by cells called somatotrophs. These and all other pituitary cells respond to the release of precursor hormones from the hypothalamus by increasing or decreasing the amount of the hormone they produce. The hypothalamus sends precursors or “releasing hormones” to the pituitary gland by secreting them into its blood vessels. The precursor to growth hormone is called growth hormone releasing hormone (SRH). The hypothalamus secretes SRH whenever the body needs more growth hormone in circulation.
Various physiological states alert the hypothalamus to the need for increased growth hormone production, such as age, diet, gender, physical activity, and hormone levels. The time of day is also important, because more growth hormone is secreted during sleep than during waking hours. Somatotropin production is slowed or stopped when the hypothalamus releases the hormone somatostatin; an increase in the concentration of GH in the bloodstream leads to the release of somatostatin from the hypothalamus, which in turn causes the anterior pituitary to stop secreting GH.
A synthetic version of somatotropin is called human growth hormone (HGH) or somatropin. It is a recombinant protein produced using molecular biology technology; previously, growth hormone was obtained from the pituitary glands of cadavers. Somatropin is used by some athletes as an anabolic steroid to enhance athletic performance, to help muscles recover more quickly from injury, and to increase the ratio of lean muscle mass to fat. There is no scientific consensus that HGH increases strength, only that it promotes muscle growth.
HGH is used clinically to treat children who do not produce enough GH in their bodies for normal growth. Children who have somatotropin deficiencies typically have short stature and often appear younger than they are. The disease can also delay the onset of puberty. HGH treatment reverses this condition.
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