Thyrotropin-releasing hormone
Encyclopedia
Thyrotropin-releasing hormone (TRH), also called thyrotropin-releasing factor (TRF), thyroliberin or protirelin, is a tropic
Tropic hormone
Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary...

 tripeptide hormone
Peptide hormone
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.Like other proteins, peptide hormones are synthesized in cells from amino acids according to an mRNA template, which is itself synthesized from a DNA template inside the...

 that stimulates the release of thyroid-stimulating hormone
Thyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...

 and prolactin
Prolactin
Prolactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...

 by the anterior pituitary
Anterior pituitary
A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland...

. TRH has been used clinically for the treatment of spinocerebellar degeneration and disturbance of consciousness in humans.

Synthesis

TRH is produced by the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

 in medial neurons of the paraventricular nucleus
Paraventricular nucleus
The paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...

. At the beginning, it is synthesized as a 242-amino acid precursor polypeptide that contains 6 copies of the sequence -Glu-His-Pro-Gly-, flanked by di-basic peptides that are later processed through proteolysis to give the mature TRH molecule.

It travels across the median eminence
Median eminence
The median eminence is part of the inferior boundary for the hypothalamus part of the human brain. A small swelling on the tuber cinereum posterior to the infundibulum - atop the pituitary stalk - the median eminence lies in the area roughly bounded on its posterolateral region by the cerebral...

 to the anterior pituitary gland via the hypophyseal portal system
Hypophyseal portal system
The hypophyseal portal system is the system of blood vessels that link the hypothalamus and the anterior pituitary in the brain.It allows endocrine communication between the two structures. It is part of the hypothalamic-pituitary-adrenal axis. The anterior pituitary receives releasing and...

 where it stimulates the release of thyroid-stimulating hormone
Thyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...

 from cells called thyrotrope
Thyrotrope
Thyrotropes are endocrine cells in the anterior pituitary which produce thyroid stimulating hormone in response to thyrotropin releasing hormone .Thyrotropes appear basophilic in histological preparations....

s and excess levels inhibit dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...

, which stimulates the release of prolactin
Prolactin
Prolactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...

, which in turn decreases GnRH.

TRH can also be detected in other areas of the body including the gastrointestinal system and pancreatic islets
Islets of Langerhans
The islets of Langerhans are the regions of the pancreas that contain its endocrine cells. Discovered in 1869 by German pathological anatomist Paul Langerhans at the age of 22, the islets of Langerhans constitute approximately 1 to 2% of the mass of the pancreas...

, as well as in the brain.

History

The sequence of TRH was first determined, and the hormone synthesized, by Roger Guillemin
Roger Guillemin
Roger Charles Louis Guillemin received the National Medal of Science in 1976, and the Nobel prize for medicine in 1977 for his work on neurohormones, sharing the prize that year with Andrew Schally and Rosalyn Sussman Yalow.Completing his undergraduate work at the University of Burgundy, Guillemin...

 and Andrew V. Schally in 1969. Both parties insisted their labs determined the sequence first: Schally first suggested the possibility in 1966, but abandoned it after Guillemin proposed TRH was not actually a peptide. Guillemin's chemist began concurring with these results in 1969, as NIH threatened to cut off funding for the project, leading both parties to return to work on synthesis.

Schally and Guillemin shared the 1977 Nobel Prize in Medicine  "for their discoveries concerning the peptide hormone production of the brain." News accounts of their work often focused on their "fierce competition" and use of a very large amount of sheep and pig brains to locate the hormone.

Chemical properties

Its molecular weight is 359.5 Da
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...

. Its tripeptide structure is: (pyro)Glu-His-Pro-NH2

Clinical significance

It is used in pharmacology (brand name Relefact TRH) to test the response of the anterior pituitary gland.

Medical preparations of TRH are used in diagnostic tests of thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...

 disorders and in acromegaly
Acromegaly
Acromegaly is a syndrome that results when the anterior pituitary gland produces excess growth hormone after epiphyseal plate closure at puberty...

.

A TRH test
TRH test
A TRH test may be indicated if secondary hypothyroidism is suspected. Some patients may have low levels of circulating thyroid hormones and secondary hypothyroidism as a result of damage to the hypothalamic or pituitary control mechanisms that regulate thyroid function...

 may be indicated if secondary hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...

is suspected.

Related peptides

TRH belongs to a family of several thyrotropin-releasing hormones (TRH).
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