A hormone (a polypeptide), secreted by the front lobe of the pituitary gland in vertebrates with jaws, which stimulates body growth through its effects on protein, carbohydrate, and lipid metabolism; also known as somatotrophin or somatotrophic hormone. It is species-specific in its actions. Its abnormal secretion may result in dwarfism, gigantism, or acromegaly (the abnormal enlargement of the facial features, hands, and feet).
Growth hormone (GH or somatotropin) is a polypeptide hormone synthesised and secreted by the anterior pituitary gland which stimulates growth and cell reproduction in humans and other vertebrate animals.
This article describes human growth hormone physiology, with brief mentions of the diseases of GH deficiency, GH excess (acromegaly and pituitary gigantism), as well as GH treatment, and HGH quackery.
Terminology
Growth hormone (GH) is also called somatropin and somatotropin (British: somatotrophin). hGH refers to human growth hormone and is an abbreviation for human GH measured in the extracts from human pituitary glands. In 1985, biosynthetic human growth hormone replaced pituitary-derived human growth hormone for therapeutic use in the U.S. and elsewhere. Biosynthetic human growth hormone, also referred to as recombinant human growth hormone, is also called somatropin and abbreviated as rhGH. See articles on GH treatment and hGH quackery for fuller discussions of GH therapy and the HGH issue.
Structure and gene of the human GH molecule
The genes for human growth hormone are localized in the q22-24 region of chromosome 17 and are closely related to human chorionic somatomammotropin (hCS, also known as placental lactogen) genes. GH, human chorionic somatomammotropin (hCS), and prolactin (PRL) are a group of homologous hormones with growth-promoting and lactogenic activity. Despite marked structural similarities between growth hormone from different species, only human and primate growth hormones have significant effects in humans.
Secretion of GH
GH is secreted into the blood by the somatotrope cells of the anterior pituitary gland, in larger amounts than any other pituitary hormone. Failure of development of these cells, as well as destruction of the anterior pituitary gland, results in GH deficiency.
Peptides released by neurosecretory nuclei of the hypothalamus into the portal venous blood surrounding the pituitary are the major controllers of GH secretion by the somatotropes. Growth hormone releasing hormone (GHRH) from the arcuate nucleus and ghrelin promote GH secretion, and somatostatin from the periventricular nucleus inhibits it. GH secretion is also affected by negative feedback from circulating concentrations of GH and IGF-1.
Although the balance of these stimulating and inhibiting peptides determines GH release, this balance is affected by many physiological stimulators and inhibitors of GH secretion. Stimulators of GH secretion include (among others) J B B , exercise, hypoglycemia, dietary protein, and estradiol. In addition to control by endogenous processes, a number of foreign compounds (xenobiotics) are now known to influence GH secretion, highlighting the fact that the GH-IGF axis is an emerging target for certain endocrine disrupting chemicals - see endocrine disruptor.
Most of the physiologically important GH secretion occurs as several large pulses or peaks of GH release each day.
The amount and pattern of GH secretion change throughout life.
Several molecular forms of GH circulate. Much of the growth hormone in the circulation is bound to a protein (growth hormone binding protein, GHBP) which is derived from the growth hormone receptor.
Functions of GH
Effects of growth hormone on the tissues of the body can generally be described as anabolic (building up). Like most other protein hormones GH acts by interacting with a specific receptor on the surface of cells.
Height growth in childhood is the best known effect of GH action, and appears to be stimulated by at least two mechanisms. GH also stimulates production of insulin-like growth factor 1 (IGF1, formerly known as somatomedin C), a hormone homologous to proinsulin.
Although height growth is the best known effect of GH, it serves many other metabolic functions as well.
Clinical problems: too much and too little
Growth hormone excess: (acromegaly and pituitary gigantism)
The most common disease of GH excess is a pituitary tumor comprised of somatotroph cells of the anterior pituitary.
Prolonged GH excess thickens the bones of the jaw, fingers and toes. It is extremely rare for such a tumor to occur in childhood, but when it does the excessive GH can cause excessive growth, traditionally referred to as pituitary gigantism.
Growth hormone deficiency (GHD)
Deficiency of GH produces significantly different problems at various ages. In children, growth failure and short stature are the major manifestations of GH deficiency.
There are many causes of GH deficiency, including mutations of specific genes, congenital malformations involving the hypothalamus and/or pituitary gland, and damage to the pituitary from injury, surgery or disease.
Diagnosis of GH deficiency involves a multiple step diagnostic process, usually culminating in GH stimulation test(s) to see if the patient's pituitary gland will release a pulse of GH when provoked by various stimuli.
GH deficiency is treated by replacing GH. All GH in current use is a biosynthetic version of human GH, manufactured by recombinant DNA technology. When the patient has had a long-standing deficiency of GH, benefits of treatment are often dramatic and gratifying and side effects of treatment are rare.
GH is used as replacement therapy in adults with GH deficiency of either childhood-onset (after completing growth phase) or adult-onset (usually as a result of an acquired pituitary tumor).
This topic is treated more fully in the articles growth hormone deficiency and growth hormone treatment.
Other GH uses and treatment indications
Many other conditions besides GH deficiency cause poor growth, but growth benefits (height gains) are often poorer than when GH deficiency is treated. Examples of other causes of shortness often treated with growth hormone are Turner syndrome, chronic renal failure, Prader-Willi syndrome, intrauterine growth retardation, and severe idiopathic short stature.
Sometimes GH is used for other benefits than height. GH treatment improves muscle strength and slightly reduce body fat in Prader-Willi syndrome, benefits more important to these children than increased height.
Uses that are controversial include
GH treatment to reverse effects of aging in older adults GH treatment to enhance weight loss in obesity GH treatment for fibromyalgia GH treatment for Crohn's disease and ulcerative colitis GH treatment for idiopathic short stature GH treatment for bodybuilding or athletic enhancementRisks and side effects of GH treatment
The possible risks and side effects of GH use are varied. They include:
swelling of the hands and feet(edema) thickening of the bones/jaw carpal tunnel syndrome/Arthralgia tingling in the extremities numbness in the hands and feet increased organ growth decreased insulin reception acromegaly decreased thyroid outputHistory
The identification, purification and later synthesis of growth hormone is associated with Choh Hao Li. The history of GH use, from extraction of GH from human pituitary glands to the limited catastrophe of Creutzfeldt-Jakob Disease to the expanded use and enormous costs of synthetic GH is outlined in the article on GH treatment.
HGH quackery
Consumers should understand that use of the term "HGH" by marketers since 1990 is a nearly infallible sign that a product so labeled contains no effective amount of growth hormone.
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