Releasing hormones and inhibiting hormones are

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

s whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are also called liberins () and statins () (respectively), or releasing factors and inhibiting factors. The principal examples are hypothalamic-pituitary hormones that can be classified from several viewpoints: they are hypothalamic hormones (originating in the

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

), they are hypophysiotropic hormones (affecting the hypophysis, that is, the

pituitary gland The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the human brain, brain, protruding off the bottom of the hypothalamus. The pituitary gland and the hypothalamus contr ...

), and they are

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. The hypothalamus secretes tropic hormones that target the anterior pituitary, and the thyroid ...

s (having other

endocrine gland The endocrine system is a network of glands and organs located throughout the body. Along with the nervous system, it makes the neuroendocrine system, which controls and regulates many of the body's functions. Endocrine glands are ductless gland ...

s as their target). For example,

thyrotropin-releasing hormone Thyrotropin-releasing hormone (TRH) is a hypophysiotropic hormone produced by neurons in the hypothalamus that stimulates the release of thyroid-stimulating hormone (TSH) as well as prolactin from the anterior pituitary. TRH has been used ...

(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 The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans, it is a butterfly-shaped gland located in the neck below the Adam's apple. It consists of two connected lobes. The lower two thirds of the lobes are connected by ...

hormones T4 and T3. When the level of TSH is 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 Prolactin (PRL), also known as lactotropin and mammotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secr ...

from this gland. The main releasing hormones are as follows: * The hypothalamus uses

(TRH or thyroliberin) to tell the pituitary to release thyrotropin. * The hypothalamus uses

corticotropin-releasing hormone Corticotropin-releasing hormone (CRH) (also known as corticotropin-releasing factor (CRF) or corticoliberin; corticotropin may also be spelled corticotrophin) is a peptide hormone involved in stress responses. It is a releasing hormone that b ...

(CRH or corticoliberin) to tell the pituitary to release

corticotropin Adrenocorticotropic hormone (ACTH; also adrenocorticotropin, corticotropin) is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important c ...

. * The hypothalamus uses

gonadotropin-releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and rele ...

(GnRH or gonadoliberin) to tell the pituitary to release

gonadotropin Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. They are central to the complex endocrine system that regulates normal growth, sexual development, and reproductive function. T ...

. * The hypothalamus uses

growth hormone–releasing hormone Growth hormone–releasing hormone (GHRH), also known as somatocrinin among other names in its endogenous form and as somatorelin (INN) in its pharmaceutical form, is a releasing hormone of growth hormone (GH). It is a 44-amino acid peptide hor ...

(GHRH or somatoliberin) to tell the pituitary to release somatotropin. The main release-inhibiting hormones or inhibiting hormones are as follows: * The hypothalamus uses

somatostatin Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or by #Nomenclature, several other names, is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G ...

to tell the pituitary to inhibit somatotropin and to tell the gastrointestinal tract to inhibit various

gastrointestinal hormone The gastrointestinal hormones (or gut hormones) constitute a group of hormones secreted by enteroendocrine cells in the stomach, pancreas, and small intestine that control various functions of the digestive organs. Later studies showed that most ...

s. There are various other inhibiting factors that also have tropic endocrine inhibition activity. Such activity is only one of many functions that they have (such as

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

and

receptor antagonist A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of rec ...

roles), and they are not always called hormones, although many are

neuropeptide Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

s or

neurosteroid Neurosteroids, also known as neuroactive steroids, are endogenous or exogenous steroids that rapidly alter neuronal excitability through interaction with ligand-gated ion channels and other cell surface receptors. The term ''neurosteroid'' was coi ...

s. They include the following: * The hypothalamus uses

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. It is an amine synthesized ...

as a prolactostatin to tell the pituitary to inhibit

; it is also created elsewhere in the brain and the

adrenal cortex The adrenal cortex is the outer region and also the largest part of the adrenal gland. It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis. Each zone is responsible for producing specific hormones. I ...

as a

to affect many other systems. * The hypothalamus uses RFRP-3 in mammals or GnIH in avian species to inhibit GnRH. * The hypothalamus uses

follistatin Follistatin, also known as activin-bindings protein, is a protein that in humans is encoded by the ''FST'' gene. Follistatin is an autocrine glycoprotein that is expressed in nearly all tissues of higher animals. Its primary function is the b ...

to tell the pituitary to inhibit

follicle-stimulating hormone Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, puberty, pubertal maturat ...

; it also has many other systemic effects. *

Myocyte A muscle cell, also known as a myocyte, is a mature contractile Cell (biology), cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal muscle, skeletal, smooth muscle, smooth, and Cardiac muscle, cardiac ...

s use

myostatin Myostatin (also known as growth differentiation factor 8, abbreviated GDF8) is a protein that in humans is encoded by the ''MSTN'' gene. Myostatin is a myokine that is produced and released by myocytes and acts on muscle cells to inhibit muscle ...

to tell each other to inhibit

myogenesis Myogenesis is the formation of skeletal muscle, skeletal muscular tissue, particularly during embryonic development. Skeletal muscle#Skeletal muscle cells, Muscle fibers generally form through the fusion of precursor cell, precursor myoblasts in ...

. * Melanocyte-inhibiting factor (melanostatin) inhibits release of other neuropeptides such as alpha-MSH and also has many other functions. * There is a neuropeptide called cortistatin and a class of steroidal cortistatins. Examples of releasing and inhibiting hormones for exocrine hormones are

gastrin-releasing peptide Gastrin-releasing peptide GRP, is a neuropeptide, a regulatory molecule encoded in the human by the ''GRP'' gene. GRP has been implicated in a number of physiological and pathophysiological processes. Most notably, GRP stimulates the release of g ...

(GRP) and

gastric inhibitory polypeptide Gastric inhibitory polypeptide (GIP), also known as glucose-dependent insulinotropic polypeptide, is an inhibiting hormone of the secretin family of hormones. While it is a weak inhibitor of gastric acid secretion, its main role, being an incr ...

(GIP), which regulate

gastrin Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas. ...

production.

Mechanism

Releasing hormones increase (or, in case of inhibitory factors, decrease) the intracellular concentration of calcium (Ca²⁺), resulting in vesicle fusion 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 G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related ...

coupled to the G_q 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.

Notable researchers

Roger Guillemin Roger Charles Louis Guillemin (; January 11, 1924 – February 21, 2024) was a French-American neuroscientist. He received the National Medal of Science in 1976, and the Nobel Prize in Physiology or Medicine, Nobel Prize for Medicine in 1977 for ...

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 A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

References

{{reflist Hormones Neuroendocrinology

Mechanism

Notable researchers

See also

References