Thyrotropin, or TRH/thyrotropin releasing hormone is a tripeptidal, tropic hormone released by the hypothalamus and which stimulates the pituitary gland to secrete the thyroid stimulating hormone or TSH and prolactin. TRH is also referred to by other names such as protirelin, thyroliberin, or TRF/thyrotropin releasing factor.
In clinical settings, thyrotropin is used for treating consciousness disturbance in humans and spino-cerebellar deterioration and degeneration.
Functions of thyrotropin
The building blocks of thyrotropin is made of a small chain of only 3 amino acids, thereby making it one of the minutest hormones in the human body. It is present in the hypothalamus and consists of a group of nerve cells referred to as the paraventricular nucleus. The hypothalamus is a section of the brain that occurs at the base of the skull, slight above the pituitary gland.
The nerve fibers which emerge from the hypothalamus carry the TRH and pass it into the bloodstream that surrounds the pituitary gland. This is where thyrotropin carries out its primary function of regulation the creation and release of TSH or thyroid stimulating hormone by the pituitary gland. Once released by the gland, the thyroid stimulating hormone helps regulate the secretion of the thyroid hormones by the thyroid gland present in the throat.
Thyrotropin or TRH has a very short lifespan and tends to last for not more than 2 minutes. It travels in the bloodstream for not more than an inch towards the pituitary gland before it gets broken down.
In addition to stimulation of pituitary gland for TSH release, the production and release of thyrotropin by the hypothalamus may also be followed by the stimulation and secretion of another hormone called prolactin by the pituitary gland. Thus, thyrotropin is instrumental in the regulating the stimulation of the pituitary gland for the release of both thyroid stimulating hormone and prolactin hormones.
Thyrotropin also widely distributes within the nervous system tissues where it may serve the purpose and function of a neurotransmitter. For example, an injection of TRH or thyrotropin can have an effect on the feeding and arousal centers of the brain, thereby leading to loss or lack of appetite and wakefulness.
Management and regulation of thyrotropin
The primary function of TRH secreted by the hypothalamus is to stimulate the production of thyrotropin which in turn stimulates the pituitary gland to release the TSH or thyroid stimulating hormone, which helps regulate the release and function of the thyroid hormones, such as triiodothyronine and thyroxine, etc., by the thyroid gland. It can thus be said that TRH is the top hormone which manages and controls the growth and function of the thyroid gland. The varied hormones released by the thyroid gland help in regulating a variety of bodily functions such as the management of body temperature, the metabolic rate, heart rate, and neuromuscular function, and production of heat, etc.
Whenever the total amount of thyroid hormone occurring in the brain dips below normal levels, the hypothalamus will detect it and release the TRH or thyrotropin into the bloodstream of the pituitary gland, which in turn will secrete additional amounts of TSH or thyroid stimulating hormone. TSH then stimulates the thyroid gland to make additional amounts of thyroid hormone which is passed to the brain, thereby ensuring that thyroid hormone present in the brain returns to normal levels.
It can thus be said that thyrotropin serves as the first messenger signal or instruction of the brain, out of the many subsequent actions that trigger the release of thyroid hormones.
Uses of thyrotropin
Thyrotropin can be used to pharmaceutically formulate a drug called ‘protirelin’ which is commonly used to test the presence of thyroid hyperactivity. A TRH test, or injections of TRH, may be carried out to verify the anterior pituitary gland’s response. It is regarded as a diagnostic test of varied thyroid ailments like secondary hypothyroidism as well as in acromegaly.
It may also be noted that currently a variety of new and more sensitive options of diagnosis and measurements are available to check underlying thyroid disorders. These new options can detect extremely low levels of TSH in the bloodstream and hence preferred by doctors. However, TSH tests have not become obsolete. They are still carried out occasionally, but often used for diagnosing conditions that occur due to resistance to the action of thyroid hormone.
Clinical tests on mice has shown that thyrotropin has anti-aging properties along with additional wide spectrum of roles. Because of this, experts believe that thyrotropin has a major role to play in the control of hormonal and metabolic functions.
Thyrotropin is also known to have anti-suicidal and anti-depressant properties.
Side effects or problems caused by thyrotropin
Very low levels of thyrotropin for prolonged periods can result in hypothyroidism or an underactive thyroid gland. It is rare and often occurs if the specific associated section of the hypothalamus has tumors or injuries. Such conditions are known as central or secondary hypothyroidism.
Intravenous administration of thyrotropin/TRH may cause minimal side effects such as increased desire to urinate frequently, flushing, minor elevation in blood pressure, and nausea, etc.