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 hormone is 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).

GH Release

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.