Growth Hormone

Growth Hormone

Growth hormone, also known as somatotropin for its growth-promoting effects on the body, also abundant hormone of the anterior pituitary. The major physiological effects of GH are anabolic: promoting protein synthesis, lipolytic, stimulating fat breakdown, lactogenic, diabetogenic by increasing resistance to insulin. Somehow, it also has intrinsic insulin-like hypoglycemic activity. Release of somatotropin from the pituitary is stimulated by the hypothalamic peptide growth hormone-releasing hormone (GHRH); somatotropin’s secretion is inhibited by somatostatin.

Growth hormone is secreted in pulses, with an average interpulse interval of 2-3 hours, with the most reproducible peak occurring at the onset of sleep. Complete absence of GH slows the rate of growth to only one third to one half of normal. Abnormally elevated levels lead to gigantism. In the adult patient with GH excess, no effects are seen in the long bones after the epiphyseal growth plates have fused. Instead, GH excess gradually produces acromegaly, a coarse thickening of the bones of the skull, hands and feet over the course of years to decades.

Functions of the Growth Hormone

Growth hormone has many diverse effects on metabolism; it is considered an amphibolic hormone because it directly influences both anabolic and catabolic processes. Increased height during childhood is the most widely known effect of GH.

Addition to increasing height in children and adolescents, growth hormone has many other effects on the body:

• Increases calcium retention, and strengthens and increases the mineralization of bone
• Increases muscle mass through sarcomere hyperplasia
• Promotes lipolysis
• Increases protein synthesis
• Stimulates the growth of all internal organs excluding the brain
• Plays a role in fuel homeostasis
• Reduces liver uptake of glucose
• Promotes gluconeogenesis in the liver
• It contributes to the maintenance and function of pancreatic islets
• It stimulates the immune system

Methods of Determination

Growth Hormone (hGH); Somatotropin

Human growth hormone (somatotropin, hGH) is essential to the growth process and has an important role in the metabolism of adults. It is secreted by the pituitary gland in response to exercise, deep sleep, hypoglycemia, glucagon, insulin and vasopressin. It also stimulates the production of RNA, and is intimately connected with insulinism. If the pituitary gland secretes too little or too much hGH in the growth phase of life, dwarfism of gigantism will result, respectively. An excess of growth hormone ducring adulthood leads to acromegaly.

This test confirms hypopituitarism or hyperpituitarism so that therapy can be initiated as soon as possible. Challenge or stimulation tests are generally used to detect hGH deficiency and are more informative. Much controversy surrounds the use of the growth hormone stimulation tests and the diagnosis should be considered in the context of the clinical picture.

Reference Values

Normal

Men: <5ng/ml or 226 pmol/L

Women: <10ng/ml or 452 pmol/L

Children: 0-20 ng/ml or 0-904 pmol/L

Newborns: 5-40 ng/ml or 226-1808 pmol/L

Stimulation test (using arginine, glucagon or insulin)

>5 ng/ml or 226 pmol/L (rise from baseline)

>10ng/ml or 452 pmol/L peak response from baseline

Suppression test (using 100 g glucose)

0-2 ng/ml or 0-90 pmol/L or undetectable

Clinical Significance

Increased hGH levels are associated with the ffg conditions:

a. Pituitary gigantism

b. Acromegaly

c. Laron’s dwarfism (hGH resistant)

d. Ectopic GH secretion

e. Uncontrolled Diabetes Milletus

Decreased hGH levels are associated with the ffg conditions:

a. Pituitary dwarfism

b. Hypopituitarism

c. Adrenocortical hyperfunction

Interferring Factors

Increased levels are associated with the use of oral contraceptives, estrogens, arginine, glucagon, levadopa, low glucose and insulin.

Levels will rise to 15 times normal by the second day of starvation; levels also rise after deep sleep, stress, exercise and anorexia.

Decreased levels are associated with obesity and the use of corticosteroids.

Many drugs interfere with the results

Recently administered interfere with the test results

Growth hormone suppression

Also called glucose loading, the growth hormone suppression test evaluates excessive baseline levels of hGH from anterior pituitary gland. Normally glucose and fatty acid aoncentrations; in response, insulin secretion increases to counteract these effects.

Purpose

-To assess elevated baseline levels of hGH

-To confirm diagnosis of gigantism in children and acromegaly in adults and adolescents

Reference Values

Normally, glucose suppresses hGH ti levels ranging from undetectable to 3 ng/ml(SI, 3 ug/L) in 30mins to 2hrs.

Abnormal findings

In a patient with active acromegaly, elevated baseline levels of hGH (5 ng/ml) aren’t suppressed to less than 5ng/ml during the test. Unchanged or rising hGH levels in response to glucose loading indicate hGH hypersecretion and may confirm suspected acromegaly and gigantism. This response may be verified the test after a 1-day rest.

Interfering factors

Failure to observe pretest restrictions

Hemolysis due to rough handling of the sample

Corticosteroids and phenothiazines such as chloropromazine

Radioactive scan performed within 1week before the test

Delay in sending the specimen to laboratory

References

John Bernard Henry 19^th edition pages 323-328

Clinical Chemistry by Michael Bishop pages 402-403

A manual of laboratory and diagnosis tests 7^th edition by frances fischbach pages 369-371

http://en.wikipedia.org/wiki/Growth_hormone#Functions_of_GH

See Picture 1 at:http://www.faqs.org/health/Body-by-Design-V1/The-Endocrine-System.htmll

See Picture 2 at: http://education.uncc.edu

See Picture 3 at: http://copland.udel.edu/~jwhite/dwarfism2.html



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