What is thyrotropin-releasing hormone?
Thyroid-releasing hormone (TRH) is a hormone produced by the hypothalamus which plays an important role in the regulation of thyroid gland activity.1
What does thyrotropin-releasing hormone do?
Made up of just three amino acid components, its main purpose is to stimulate the release of thyrotropin also known as thyroid stimulating hormone (TSH). Nerve fibres carry TRH to the blood supply surrounding the pituitary gland where it is then broken down. The hormone is used to regulate the formation and release of TSH, which in turn regulates the production of thyroid hormones in the thyroid gland itself.1
TRH is responsible for controlling various functions in our bodies including energy homeostasis, feeding behaviour, thermogenesis, metabolic rate, heat generation, neuromuscular function, heart rate and autonomic regulation.1
It can stimulate the release of prolactin, another hormone from the pituitary gland and may also act as a neurotransmitter in the tissues of the nervous system – a TRH injection affects the arousal and feeding centres of the brain, causing wakefulness and loss of appetite.
When does thyrotropin-releasing hormone cause problems?
When someone produces too little TRH they will develop a condition called hypothyroidism – underactivity of the thyroid. In the situation where injury or illness attacks the hypothalamus resulting in reduced production of TRH, secondary or central hypothyroidism can occur.1
There aren’t any recorded cases of a person producing too much TRH.1
What are the symptoms?
Should a person produce too little TRH (resulting in hypothyroidism) symptoms can include:
- weight gain
- feeling the cold
- physical lethargy
- mental lethargy
- dry skin
- hair loss
- muscle cramps and/or weakness
- lowering in the tone of the voice (gruffness)
- loss of hearing
- a change in menstrual cycle for women
- puffiness around the eye area
- some people may experience physical changes in the size of their thyroid gland that can be seen externally
It is important to note that symptoms can vary dramatically between patients.2 If you have any of these symptoms you would require a medical assessment to obtain a diagnosis.
Why and how to be tested
If you are concerned that you are producing too little TRH and suffering from symptoms of possible hypothyroidism it is important to seek professional medical advice.
Your clinician will discuss your medical history with you, carry out a physical examination and arrange for specific blood tests to be done, one of which – a TRH stimulation test – may need to be carried out in the outpatient department of your local hospital because it’s what is called a “dynamic” test. Dynamic testing is where a hormone is stimulated by a chemical – in this case TRH.
Tests for TRH concerns should not be carried out on pregnant women. Patients on a thyroxine prescription should not take their medication for 3 weeks prior to TRH tests.3
It is rare these days that TRH tests are carried out, but should you find yourself undergoing the test it should take around 2 hours and it will be carried out by an endocrine nurse specialist.
The nurse will place a small plastic tube into a vein in your arm, which will be used to take blood samples and to give you an injection of TRH. First, you will have a baseline blood test to measure your TRH levels. Following this initial test, you will be given a dose of TRH into your vein, through the tube that is in place. This works to stimulate your pituitary gland to release TRH. Further blood samples are then taken during the following 60 minutes after pituitary stimulation to ascertain comparative levels of TRH.
You may experience some side effects following the TRH injection including flushing, dizziness, nausea, increased heart rate, a strange taste in your mouth and the need to pass urine. Very rarely some people experience wheeziness. These side effects should only last around 5 minutes. Once all the tests have been completed you will be able to return home.3
If your TRH test shows up a problem, you will be given treatment for hypothyroidism.
The prognosis for this condition is good as thyroid hormone treatment usually resolves all symptoms as long as you are on the correct treatment and/or correct dosage.
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Homeostasis – the ability of the body to maintain a stable internal environment despite changes in external conditions
Hypothalamus – a small area at the base of the brain where the pituitary gland is found, and helps regulate the endocrine and nervous system
Hypothyroidism – a term used to describe an under-active thyroid gland
Neuromuscular – relating to nerves and muscles
Pituitary gland – the major endocrine gland, a pea-sized body attached to the base of the brain that is important in controlling growth and development and the functioning of the other endocrine glands
Thermogenesis – the production of heat, especially in a human or animal body
Thyrotropin (TSH) – a hormone secreted by the pituitary gland which regulates the production of thyroid hormones
- You and Your Hormones – Thyrotropin-releasing hormones
- You and Your Hormones – Hypothyroidism
- Leeds Pathology – Thyroid-releasing hormone (TRH) test
Date updated: 24/02/20 (V1.1)
Review date: 18/10/20