Growth hormone-releasing factor; GRF; GHRF; GHRH
Growth hormone-releasing hormone is a hormone produced in the hypothalamus. The principal function of growth hormone-releasing hormone is to stimulate the pituitary gland to produce and release growth hormone into the bloodstream. This then acts on virtually every tissue of the body to control several physical functions and processes. Insulin-like growth factor 1 is a hormone produced in the liver and other organs in response to growth hormone, which in turn acts in many tissues to cause metabolic and growth actions. In addition to its effect on growth hormone secretion, growth hormone-releasing hormone also affects sleep, food intake and memory.
The action of growth hormone-releasing hormone on the pituitary gland is counteracted by somatostatin, a hormone also produced by the hypothalamus, which prevents growth hormone release.
In order to maintain a balanced hormone production, growth hormone-releasing hormone, somatostatin, growth hormone and insulin-like growth factor 1 levels are regulated by each other. The consequence of growth hormone-releasing hormone action is an increase in the circulating levels of growth hormone and insulin-like growth factor 1 which, in turn, act back on the hypothalamus to prevent growth hormone-releasing hormone production and to stimulate somatostatin secretion. Somatostatin then prevents the release of growth hormone from the pituitary gland and growth hormone-releasing hormone production by the hypothalamus, therefore acting as a powerful suppressor of growth hormone secretion.
Many other factors and physiological conditions such as sleep, stress, exercise and food intake also affect the hypothalamic release of growth hormone-releasing hormone and somatostatin.
Too much growth hormone-releasing hormone production may be caused by hypothalamic tumours or by tumours located in other parts of the body (ectopic tumours). The consequence of too much growth hormone-releasing hormone is a rise in growth hormone levels in the bloodstream and, in many cases, enlargement of the pituitary gland.
In adults, excessive growth hormone for a long period of time produces a condition known as acromegaly in which patients have swelling of the hands and feet and altered facial features. These patients also have organ enlargement and serious functional disorders such as high blood pressure, diabetes and heart disease. An increase in growth hormone before children reach their final height can lead to excessive growth of long bones, resulting in the child being abnormally tall. This is commonly known as gigantism.
However, in most cases, growth hormone overproduction is caused by pituitary tumours that produce growth hormone; only in very rare occasions is excess growth hormone caused by overproduction of growth hormone-releasing hormone.
If the hypothalamus produces too little growth hormone-releasing hormone, the production and release of growth hormone from the pituitary gland is impaired, leading to a lack of growth hormone (adult-onset growth hormone deficiency). When a deficiency of growth hormone is suspected, a ‘growth hormone stimulating test’ is performed using growth hormone-releasing hormone or other substances, in order to determine the ability of the pituitary gland to release growth hormone.
Childhood-onset growth hormone deficiency is associated with growth failure and delayed physical maturity. In adults, the most important consequences of reduced growth hormone levels are changes in body structure (decreased muscle and bone mass and increased body fat), tiredness, being less lively and a poor health-related quality of life.
Last reviewed: Dec 2014