It is one of the smallest hormones in the body, consisting of a miniature chain of just three building blocks of amino acids.
Alternative names for this hormone:
- Thyrotropin-releasing hormone.
It is made up of a group of nerve cells in the hypothalamus, an area at the base of the brain just above the pituitary gland.
This group of nerve cells is known as the paraventricular nucleus. The nerve fibers emerging from it carry thyrotropin-releasing hormone and release it into the blood surrounding the pituitary gland, where it has its most important action.
This is to regulate the formation and secretion of thyroid stimulating hormone in the pituitary gland, which in turn regulates the production of thyroid hormones in the pituitary gland.
Thyrotropin-releasing hormone is very short-lived, lasting about two minutes, and travels less than an inch in the bloodstream to the pituitary gland before it breaks down.
Thyrotropin-releasing hormone (TRH) was originally isolated from the hypothalamus.
Functions of the hormone TRH
In addition to controlling TSH secretion from the anterior pituitary, this tripeptide is widely distributed in the central nervous system and is considered as a neurotransmitter or modulator of neuronal activities in the extrahypothalamic regions, including the cerebellum.
HRT plays an important role in the regulation of energy homeostasis, eating behavior, thermogenesis, and autonomic regulation.
HRT controls energy homeostasis primarily through its hypophysiotropic actions to regulate circulating levels of thyroid hormones.
Recent research has revealed that TRH production is directly regulated at the transcriptional level by leptin, one of the adipocytokines that plays a critical role in diet and energy expenditure.
Improved ataxic gait is one of the important pharmacological properties of HRT. In the cerebellum, cyclic GMP has been shown to be involved in the effects of TRH.
Thyrotropin-releasing hormone secretion by the hypothalamus can also stimulate the release of another hormone from the pituitary gland, prolactin.
In addition to its role in controlling thyroid stimulating hormone and prolactin release, thyrotropin-releasing hormone has a wider distribution in nervous system tissues where it can act as a neurotransmitter.
For example, an injection of thyrotropin-releasing hormone has effects on the brain’s activation and feeding centers, causing wakefulness and loss of appetite.
How is thyrotropin-releasing hormone controlled?
As its name implies, the main effect of thyrotropin-releasing hormone is to stimulate the release of thyrotropin (also known as thyroid-stimulating hormone) from the pituitary gland.
Thyrotropin-releasing hormone is the main regulator of growth and function of the thyroid gland (including the secretion of the thyroid hormones thyroxine and triiodothyronine).
These hormones control the body’s metabolic rate, heat generation, neuromuscular function, and heart rate, among other things. If there is not enough thyroid hormone available to the brain, the hypothalamus will detect it and thyrotropin-releasing hormone will be released into the blood that supplies the pituitary gland.
The effect of thyrotropin-releasing hormone on the pituitary gland is to trigger the release of thyroid-stimulating hormone, which in turn stimulates the thyroid gland to produce more thyroid hormone.
In summary, thyrotropin-releasing hormone is the brain’s first messenger signal in the many actions that control thyroid hormone secretions.
Thyrotropin-releasing hormone (in its pharmaceutical formulation ‘ protirelin ‘) has been widely used as a drug to assess whether someone has an overactive thyroid. However, there are now more sensitive measurements that can detect very low levels of thyroid stimulating hormone in the blood.
Thyrotropin-releasing hormone tests are still done occasionally, but are typically used to diagnose conditions caused by resistance to the action of thyroid hormone.
What if I have too much thyrotropin-releasing hormone?
Thyrotropin-releasing hormone excess is not known.
What if I have too little thyrotropin-releasing hormone?
If a person has too little thyrotropin-releasing hormone, they will develop an underactive thyroid (hypothyroidism). This is a rare condition, usually due to an injury or tumor that destroys this area of the hypothalamus. This situation is known as secondary or central hypothyroidism.