Alternative names for growth hormone-releasing hormone
Growth hormone-releasing factor; GRF; GHRF; GHRH
What is growth hormone-releasing hormone?
Growth hormone-releasing hormone is a type of hormone that is produced in a small part of the brain, called the hypothalamus. The main role of growth hormone-releasing hormone is to stimulate another part of the brain, the pituitary gland, to produce and release growth hormone into the bloodstream.
Growth hormone acts on virtually every tissue of the body to control metabolism and growth. Metabolism is our body’s process of converting food into energy that is needed to carry out all of the body’s functions. Growth hormone also stimulates the production of another hormone, the insulin-like growth factor-1 (IGF-1) in the liver and other organs which also acts on tissues in the body to control metabolism and growth. 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, another hormone also produced by the hypothalamus, which prevents growth hormone release.
Release and function of growth hormone-releasing hormone. Made in Biorender
How is growth hormone-releasing hormone controlled?
The body controls the release of growth hormone-releasing hormone and growth hormone as part of a feedback loop. Here is how it works:
- The hypothalamus releases the growth hormone-releasimg hormone.
- The growth hormone-releasing hormone acts on the pituitary gland to trigger the release of growth hormone.
- A rise in growth hormone levels feedbacks to the hypothalamus instructing it to stop making or decrease the levels of growth hormone-releasing hormone.
- The rise in growth hormone levels, also stimulates the liver and other parts of the body to produce IGF-1. IGF-1 also feedbacks to the hypothalamus, instructing it to stop making growth hormone releasing hormone.
- In response to the rise of growth hormone and IGF-1, the body also produces another hormone called somatostatin. Somatostatin acts like a brake, stopping the body from making more growth hormone. To do this, it works on the hypothalamus to stop the growth hormone-releasing hormone and also on the pituitary to stop the growth hormone release.
In summary, in order to maintain a normal balance, growth hormone-releasing hormone, somatostatin, growth hormone and IGF-1 levels are regulated by each other.
Many other factors also affect the release of growth hormone-releasing hormone and somatostatin. These include sleep, stress, exercise, and food intake.
What happens if I have too much growth hormone-releasing hormone?
Too much growth hormone-releasing hormone production may be caused by small growths in the hypothalamus known as adenomas, or rarely by growths (tumours) located in other parts of the body (known as ectopic tumours). Both of these types of growths are very rare. You can also get small growths in the pituitary gland, which lead to excessive production of growth hormone (called pituitary adenomas). These are more common than hypothalamic growths.
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 children, too much growth hormone during puberty and before they have reached their final height can lead to excessive growth of long bones, resulting in the child being abnormally tall. This is commonly known as gigantism.
In adults, excessive growth hormone for a long period of time produces a condition known as acromegaly in which patients have excessive growth of the hands and feet and altered facial features. These patients are also at risk of high blood pressure and high blood sugar (also known as glucose) levels, which can lead to diabetes. They also get organ enlargement, including of the heart muscle which can lead to heart disease.
You can diagnose excessive growth hormone release based on the symptoms and signs, by checking blood levels of IGF-1, and by carrying out a test known as a glucose tolerance test. Glucose (also known as sugar) makes growth hormone levels drop in normal people. If levels don't drop, it suggests there is an excess of growth hormone. After this, doctors can use an MRI scan to look at the pituitary gland to check if a tumour is causing the high growth hormone production.
When someone has too much growth hormone, doctors use different treatments to bring it back to normal levels. The main options include surgery to remove the tumour, medication that can lower growth hormone production or block its effects, or radiotherapy when surgery or medicine do not work well enough.
What happens if I have too little growth hormone-releasing hormone?
When the hypothalamus does not produce enough growth hormone-releasing hormone, it affects the pituitary gland’s ability to produce and release growth hormone. This can lead to a condition called growth hormone deficiency.
Doctors may suspect growth hormone deficiency based on symptoms like slow growth in children, or certain health issues such as tiredness in adults. When a deficiency of growth hormone is suspected, doctors can carry out a ‘growth hormone stimulating test’ using different hormones to check if the pituitary gland can produce growth hormone when stimulated. Doctors can use various substances for this test which normally trigger growth hormone release from the pituitary gland. These substances may include insulin or growth hormone-releasing hormone itself.
A normal pituitary gland should respond by producing growth hormone. If growth hormone levels do not rise sufficiently, this suggests growth hormone deficiency. This could be due to problems with the pituitary gland itself or issues with the hypothalamus not producing enough growth hormone-releasing hormone. Additional tests may be needed to find the exact cause and location of the problem, which include an MRI imaging scan of the brain.
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.
The main treatment for growth hormone deficiency is growth hormone replacement therapy.