Human Growth Hormone
Human growth hormone
Human growth hormone (GH), also called somatotropin, is a protein that stimulates growth. GH must be secreted (released) in just the right amount in a child for normal growth to take place. If too litle is human growth hormoneis produced, the child will become a dwarf; if too much is secreted, the child will grow to be a giant.
GH is secreted by the anterior pituitary gland, located at the base of the brain. The pituitary has a direct effect on the metabolism of proteins, carbohydrates, and lipids and controls the growth rate of the skeleton and internal organs.
Gigantism and Acromegaly
The notion of a growth hormone arose from clinical observations on gigantism and acromegaly. Gigantism is a condition caused by too much GH in childhood and marked by much greater height than usual. Acromegaly is caused by too much GH in adulthood and is marked by a thickening of the bones in the feet, hands, and face. In the 1930s, American biologist Herbert Evans (1882-1971) demonstrated how extracts from the pituitary gland can greatly stimulate animal growth, producing gigantism.
In the 1940s, Evans and his colleague Choh Hao Li isolated the growth hormone from cattle. Other scientists isolated growth hormones in different animal species. In 1970, Li and other scientists independently synthesized GH using genetic engineering techniques. This led to the first production of genetically engineered human growth hormone in the 1980s by Eli Lilly and Company and Genentech (a bio-research organization).
Lack of normal amounts of GH during childhood can result in a type of dwarfism in which the person is small but has normal proportions and intelligence. Injections of GH can achieve remarkable results and help the person reach normal or near-normal size if the condition is diagnosed while the bones can still grow (before the long bones have closed).
The pituitary releases GH when it receives a signal from the brain's hypothalamus in the form of growth hormone releasing hormone (GHRH). Release, however, can also be triggered by stress, exercise, emotional excitement, fasting, sleep, or hypoglycemia (low blood sugar). Release is inhibited by the hormone somatostatin and may be inhibited by lack of sleep, high blood sugar (hyperglycemia), obesity, a high blood level of free fatty acids, and by growth hormone itself. American endocrinologist Roger Guillemin and colleagues isolated somatostatin in 1973 and growth hormone releasing hormone (at that time called growth hormone releasing factor; now known to be a hormone) in 1984.
The pharmaceutical firm of Hoffmann-La Roche announced in 1989 that it had developed an artificially produced growth hormone releasing hormone which, when administered, stimulates the body to produce normal amounts of growth hormone. This may have advantages for a patient because a smaller dose is required than that of growth hormone. Also, GHRH is a much smaller molecule, so it can be administered by a skin patch or inhalant, rather than by injection.
An Ethical Dilemma
Since the introduction of synthetic growth hormone in the late 1980s, a controversy has arisen over efforts to boost the growth rate of children who are on the border between being of regular height and being unusually short. Some children are simply short because their parents are. Many physicians are wary of treating short children who do not have GH deficiency just for cosmetic or social reasons. They believe the children's parents, who are short themselves, are trying to prevent their children from the failures the parents experienced as children and blame on their being short. Also, the long-term effects of such treatments are not known.
On the other side of the issue are parents, as well as some researchers, who claim that short children are socialized according to height rather than chronological age. It is claimed that they are stigmatized by abnormal appearance and have poor academic achievement, low self-esteem, and poor social skills.
Researchers in a 1994 study on the subject, reported in the journal Pediatrics, concluded that GH therapy should not be routinely administered to short children to improve their psychological health. The report urged physicians to consider both a child's short stature and psychosocial functioning before making a decision.
[See also Gene ; Hormone ]
Human Growth Factors
Human growth factors
Human growth factors are compounds made by the body that function to regulate cell division and cell survival. Some growth factors are also produced in the laboratory by genetic engineering and are used in biological therapy.
Human tumors express large amounts of growth factors and their receptors. A tumor will not grow beyond the size of a pinhead without new blood vessels to supply oxygen and nutrients. Growth factors are significant because they can induce angiogenesis, the formation of blood vessels around a tumor. These growth factors also encourage cell proliferation, differentiation, and migration on the surfaces of the endothelial cells—cells found inside the lining of blood vessels. Of the approximately 20 proteins that activate endothelial cell growth, two growth factors in particular, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), are expressed by many tumors and appear important in contributing to tumor growth and promoting tumor spread throughout the body. Several compounds that block VEGF or its receptor are now in clinical trials .
See also Angiogenesis inhibitors
Crystal Heather Kaczkowski, MSc.