Releasing hormone
Encyclopedia
A releasing hormone or releasing factor is a hormone
whose main purpose is to control the release of another hormone. The main releasing hormones secreted by the hypothalamus are:
Two other factors are also classed as releasing hormones, although they in fact inhibit pituitary hormone release
For example, TRH is released from the hypothalamus
in response to low levels of secretion of thyroid stimulating hormone (TSH) from the pituitary gland
. The TSH in turn is under feedback control by the thyroid
hormones T4
and T3
. When the levels of TSH are too high, they feed back on the brain to shut down the secretion of TRH. Synthetic TRH is also used by physicians as a test of TSH reserve in the pituitary gland as it should stimulate the release of TSH
and prolactin
from this gland.
Releasing hormones are sometimes known as liberins. For example, TRH may be known as thyroliberin. Inhibiting hormones may be known as statins. For example, dopamine (which inhibits prolactin release) may be called prolactostatin.
of the respective primary hormone.
For GnRH, TRH and GHRH the increase in Ca2+ is achieved by the releasing hormone coupling and activating G protein coupled receptors coupled to the Gq alpha subunit
, activating the IP3/DAG pathway to increase Ca2+. For GHRH, however, this is a minor pathway, the main one being the cAMP dependent pathway
.
and Andrew W. Schally were awarded the Nobel Prize in Physiology and Medicine in 1977 for their contributions to understanding "the peptide hormone production of the brain"; these scientists independently first isolated TRH and GnRH and then identified their structures
.
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
whose main purpose is to control the release of another hormone. The main releasing hormones secreted by the hypothalamus are:
- Thyrotropin-releasing hormoneThyrotropin-releasing hormoneThyrotropin-releasing hormone , also called thyrotropin-releasing factor , thyroliberin or protirelin, is a tropic tripeptide hormone that stimulates the release of thyroid-stimulating hormone and prolactin by the anterior pituitary...
(TRH), - Corticotropin-releasing hormoneCorticotropin-releasing hormoneCorticotropin-releasing hormone , originally named corticotropin-releasing factor , and also called corticoliberin, is a polypeptide hormone and neurotransmitter involved in the stress response...
(CRH), - Gonadotropin-releasing hormoneGonadotropin-releasing hormoneGonadotropin-releasing hormone , also known as Luteinizing-hormone-releasing hormone and luliberin, is a tropic peptide hormone responsible for the release of follicle-stimulating hormone and luteinizing hormone from the anterior pituitary. GnRH is synthesized and released from neurons within...
(GnRH), - Growth hormone-releasing hormone (GHRH),
Two other factors are also classed as releasing hormones, although they in fact inhibit pituitary hormone release
- SomatostatinSomatostatinSomatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.Somatostatin...
, - DopamineDopamineDopamine 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...
.
For example, TRH is released from the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
in response to low levels of secretion of thyroid stimulating hormone (TSH) from the pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
. The TSH in turn is under feedback control by the 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...
hormones T4
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
and T3
Triiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
. When the levels of TSH are too high, they feed back on the brain to shut down the secretion of TRH. Synthetic TRH is also used by physicians as a test of TSH reserve in the pituitary gland as it should stimulate the release of TSH
TSH
TSH may refer to:* Tanzanian shilling, the currency of Tanzania* Thyroid-stimulating hormone, a hormone synthesized and secreted by thyrotrope cells* Tshiuetin Rail Transportation, a Canadian railway between Labrador and Quebec...
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...
from this gland.
Releasing hormones are sometimes known as liberins. For example, TRH may be known as thyroliberin. Inhibiting hormones may be known as statins. For example, dopamine (which inhibits prolactin release) may be called prolactostatin.
Mechanism
Releasing hormones increase (or, in case of inhibitory factors, decrease) the intracellular concentration of calcium (Ca2+), resulting in vesicle fusionVesicle fusion
Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis at the porosome...
of the respective primary hormone.
For GnRH, TRH and GHRH the increase in Ca2+ is achieved by the releasing hormone coupling and activating G protein coupled receptors coupled to the Gq alpha subunit
Gq alpha subunit
Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C . PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate to diacyl glycerol and inositol triphosphate signal transduction pathway...
, activating the IP3/DAG pathway to increase Ca2+. For GHRH, however, this is a minor pathway, the main one being the cAMP dependent pathway
CAMP dependent pathway
In the field of molecular biology, the cAMP-dependent pathway, also known as the adenylyl cyclase pathway, is a G protein-coupled receptor-triggered signaling cascade used in cell communication.-Mechanism:...
.
Notable researchers
Roger GuilleminRoger 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 W. Schally were awarded the Nobel Prize in Physiology and Medicine in 1977 for their contributions to understanding "the peptide hormone production of the brain"; these scientists independently first isolated TRH and GnRH and then identified their structures
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...
.