Assignment #3: Function and Pathologies of Growth Hormone

Growth hormone is a peptide hormone that is synthesized in the anterior pituitary.

Functions:

Growth hormone has a variety of functions that are important in a vast range of species. Functions of growth hormone concern growth itself, metabolism, reproduction, immune responses, osmoregulation and more.

In mammals, growth hormone induces an increase in body weight and height (i.e growth). Growth hormone contributes to muscle growth by the combined effects of hyperplasia and hypertrophy. Hyperplasia is the process by which cell numbers increase by division and the prevention of cell death (apoptisis). Hypertrophy on the other hand is the increase in the size of cells.

Growth hormone also contributes to skeletal growth, by increasing calcuim retention, stimulating the division and multiplication of chondrocytes (cartilage cells) and increasing osteoblast (bone forming cell) activity.

Growth hormone has important effects (both direct and indirect) concerning carbohydrate, protein and lipid metabolism. Carbohydrate metabolism is affected by growth hormone in that it regulates the uptake of glucose by the liver, thus maintaining blood glucose within a certain range. Growth hormone also suppresses the actions of insulin to uptake glucose from the peripheral tissues. Protein metabolism is affected because growth hormone is a protein anabolic hormone, resulting in the increased uptake of amino acids, increased protein synthesis and decreased oxidation of proteins. Lipid (fat) metabolism relies on growth hormone because it exerts an overall lipolytic effect in which the hydrolysis of triglycerides form free fatty acids and glycerol.

Growth hormone has been termed a "cogonadotropin", and may serve a small role in both male and female reproduction. There is increasing evidence that GH can influence functioning of mammalian ovarian cells. As well, there is evidence that GH exerts a modulatory effect on reproduction in males. For example, in a study, GH was administered to preadolescent boys who progressed through puberty faster than the average male. These trends have not been confirmed for all species, nor all test subjects.

Growth hormone has been linked to the maintenance and control of the immune system. Growth hormone therapy to GH-deficient children appeared to enhance the ability of lymphocytes to proliferate.

The osmoregulatory function of GH can be seen due to the fact that renal function in mammals is affected by growth hormone. In a study reported in 1949, GH was found to have an increase on the glomular filtration rate and renal plasma flow.

Pathologies Relating to Growth Hormone:

There are many diseases associated with growth hormone excess and deficiency.

1)Acromegaly: acromegaly is the most common disease associated with excess production of growth hormone in adults. It results due to a tumor composed of somatotroph cells of the anterior pituitary. Eventually the tumor enlarges to a point that headaches and imparied vision occur due to pressure on the optic nerves. Symptoms of acromegaly include overgrowth of extremities, soft-tissue swelling, abnormalities in facial features (jaw and nose).

Figure 1: Acromegaly Disorder as it Progresses Through Time

2)Gigantism: Gigantism occurs as a result of excess growth hormone production in children or adolescents. It is usually a result from a tumor of somatotrophs. Robert Wadlow was a famous giant and when he died at the age of 22, he weighed 490 pounds and reached a height of 8 feet 11 inches.

Figure 2: Robert Wadlow: Gigantism

Treatment: Treatment for pituitary tumors causing acromegaly and gigantism include surgical removal of the tumor, focused radiation and a gowth hormone antagonist such as bromocriptine or octreotide.




3) Dwarfism: A result of GH deficiency in children results in dwarfism. Dwarfism is characterized by short stature and growth failure. In adults, GH deficiency is rare and results in deficiencies in strength, energy and bone mass. Causes are mutations of genes, congenital malformations involving the hypothalamus and/or pituitary gland. As well, damage to the pituitary from injury, surgery or disease can result in GH secretion problems.

Figure 3: Dwarfism Resulting from a GH Deficiency in a Child.

Treatment: Treatment of dwarfism involves the injection of recombinant GH from humans. In the past, GH extracted from human cadavres was used, however with modern technology, GH can be collected from recombinant DNA technology. It should also be noted that dwarfism in children cannot be reversed.

References:

[1] Cocchi, D., Locatelli, V., Muller, E.E. (Eds.). (1993). Growth Homone and Somatomedins during Lifespan. Germany: Springer-Verlag.

[2] Daughaday, W.H., Harvey, S., Scanes, C.G., (1995). Growth Hormone. Florida, USA: CRC Press.

[3] Muller, E.E., Pecile, A. (1975). Growth Hormone and Related Peptides. Amsterdam: Excerpta Medica