Therotropin-Releasing Hormone (TRH)
The simplest of thyrotropin-releasing hormones, hypothalamic neurohormones, is the three amino acids in the glutamic acid–histidine–proline sequence. The therapeutic simplicity of thyrotropin-releasing hormones is cheating because this hormone actually has many functions. This stimulates the synthesis and secretion of thyrotropin (thyroid-stimulating hormone) by the anterior pituitary gland. Given the high dose by injection, it stimulates the secretion of prolactin from the pituitary gland, although it does not seem to control the secretion of prolactin. Therotropin-releasing hormone is also found in the entire brain and spinal cord, where it is thought to act as a neuromodulator.
Thyrotropin-releasing hormone appeared very quickly in the development of vertebrae, and, while its concentration is the highest in the hypothalamus, the total amount of thyrotropin-releasing hormones in the rest of the brain is much higher in the hypothalamus. The neurotransmitters producing thyrotropin-releasing hormones in the hypothalamus are subject to stimulant and inhibitory effects from the upper centers of the brain and serum thyroid hormone concentrations, stimulating low concentrations and high concentrations inhibit the production of thyrotropin-releasing hormones. In this way, thyrotropin-releasing hormone forms the largest component of the hypothalamus-pituitary-thyroid axis. The lack of thyrotropin-releasing hormone is a rare cause of hypothyroidism. For more information about thyroid function, see thyroid gland.
What is Thyrotropin-Releasing Hormone?
Therotropin-releasing hormone is one of the smallest hormones in the body, with only a small series of three amino acids building blocks. It is formed by a group of nerve cells in the hypothalamus, which is an area on the base of the pituitary on the brain. This neural cell cluster is known as the paraventricular nucleus. Nerve fibers coming out of it take thyrotropin-releasing hormones and leave it in the blood around the pituitary gland, where its most important action is taken. This is to control the formation and secretion of thyroid stimulating hormones in the pituitary gland, which in turn regulates the production of thyroid hormones in the thyroid gland. Therotropin-releasing hormone is very rare, which is running in a matter of two minutes and it is traveling less than an inch in the blood stream in the pituitary gland before breaking it down.
Hypothalamus secretion of thyrotropin-releasing hormone can stimulate the pituitary gland, the release of another hormone from prolactin. In addition to its role in the control of thyroid stimulating hormone and prolactin release, thyrotropin-releasing hormone is a widespread distribution in the nervous system tissues where it can function as a neurotransmitter. For example, injections of thyotropin-releasing hormones affect brain stimulation and dietary centers, thereby causing awareness and lack of appetite.
How is The Thyrotropin-Releasing Hormone Regulated?
As its name implies, the main effect of thyrotropin-releasing hormone is to stimulate the release of the thyrotropin (also called thyroid stimulating hormone) from the pituitary gland. Therotropin-releasing hormone is the master regulator of thyroid gland development and function (including the secretion of the thyroid hormones thyroxine and triiodothyronine). These hormones control the body’s metabolic rate, heat production, neuromuscular function and heart rate with other things. If there is insufficient thyroid hormone for the brain, then it will be detected, the hypothalamus and thyotropin-releasing hormones will be released into the blood supply to the pituitary gland. The effect of thyrotropin-releasing hormone on the pituitary gland is to trigger thyroid stimulating hormone release, which in turn stimulates the thyroid gland and to make thyroid hormones. In essence, thyrotropin-releasing hormone is the first messenger sign in the brain in many functions that control thyroid hormone secretion.
Therotropin-releasing hormone (in the pharmaceutical formulation of ‘protirelin’) was tested to check whether the thyroid is overactive or not. However, now there are more sensitive measures which can detect very low levels of thyroid stimulating hormones in the blood. Therotropin-releasing hormone tests are still performed sometimes but are usually used to diagnose conditions due to the resistance of thyroid hormone action.
What Happens if I Have a Thyrotropin-Releasing Hormone Too Much?
There is no known case of too much thyrotropin-releasing hormone.
What Happens if I Have Very Little Thyrotropin-Releasing Hormones?
If a person has very little thyrotropin-releasing hormone, they will develop thyroid underactivity (hypothyroidism). This is a rare situation, usually due to injury or tumor that destroys this area of the hypothalamus. This condition is known as secondary or central hypothyroidism.