vasopressin receptor
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The actions of vasopressin are mediated by stimulation of tissue-specific
G protein-coupled receptor 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 p ...
s (GPCRs) called vasopressin receptors that are classified into the V1 (V1A), V2, and V3 (V1B) receptor subtypes. These three subtypes differ in localization, function and signal transduction mechanisms.


Subtypes

There are three subtypes of vasopressin receptor: V1A (V1), V1B (V3) and V2.


V1 receptor

V1 receptors (V1Rs) are found in high density on vascular smooth muscle and cause
vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vess ...
by an increase in intracellular calcium via the phosphatidyl–inositol-bisphosphate cascade. Cardiac myocytes also possess V1R. Additionally V1R are located in
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
,
testis A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...
, superior cervical ganglion,
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
,
blood vessels The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
, and renal medulla. V1R is present on
platelets Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ...
, which upon stimulation induces an increase in intracellular calcium, facilitating
thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (th ...
. Studies have indicated that due to polymorphism of platelet V1R there is significant heterogeneity in the aggregation response of normal human platelets to vasopressin. V1Rs are found in
kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
, where they occur in high density on medullary interstitial cells, vasa recta, and epithelial cells of the collecting duct. Vasopressin acts on medullary vasculature through V1R to reduce blood flow to inner medulla without affecting blood flow to outer medulla. V1Rs on the luminal membrane of the collecting duct limit the
antidiuretic An antidiuretic is a substance that helps to control fluid balance in an animal's body by reducing urination, opposing diuresis. Its effects are opposite that of a diuretic. The major endogenous antidiuretics are antidiuretic hormone (ADH; also ca ...
action of vasopressin. Additionally, vasopressin selectively contracts
efferent arterioles The efferent arterioles are blood vessels that are part of the urinary tract of organisms. Efferent (from Latin ex + ferre) means "outgoing", in this case meaning carrying blood out away from the glomerulus. The efferent arterioles form a conv ...
probably through the V1R, but not the afferent arteriole.


V2 receptor

V2 receptor (V2R) differs from V1R primarily in the number of sites susceptible to N-linked glycosylation; the V1R has sites at both the amino-terminus and at the extracellular loop, whereas the V2R has a single site at the extracellular amino-terminus. The well known
antidiuretic An antidiuretic is a substance that helps to control fluid balance in an animal's body by reducing urination, opposing diuresis. Its effects are opposite that of a diuretic. The major endogenous antidiuretics are antidiuretic hormone (ADH; also ca ...
effect of vasopressin occurs via activation of V2R. Vasopressin regulates water excretion from the kidney by increasing the osmotic water permeability of the renal collecting duct – an effect that is explained by coupling of the V2R with the Gs signaling pathway, which activates
cAMP Camp may refer to: Outdoor accommodation and recreation * Campsite or campground, a recreational outdoor sleeping and eating site * a temporary settlement for nomads * Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...
. The V2R continues to activate Gs after being internalized by β- arrestin rather than being desensitized. This internalized Gs signaling by V2R is explained by the receptors ability to form "mega-complexes" consisting of a single V2R, β-arrestin, and heterotrimeric Gs. The increased intracellular cAMP in the kidney in turn triggers fusion of aquaporin-2-bearing vesicles with the apical plasma membrane of the collecting duct principal cells, increasing water reabsorption.


V3 receptor

The human V3 receptor (V3R, previously known as V1BR) is a G-protein-coupled
pituitary In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...
receptor that, because of its scarcity, was only recently characterized. The 424-amino-acid sequence of the V3R has homologies of 45%, 39%, and 45% with the V1R, V2R and oxytocin receptor (OTR), respectively. However, V3R has a pharmacologic profile that distinguishes it from the human V1R and activates several signaling pathways via different
G-proteins G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their ac ...
, depending on the level of receptor expression.


Function

Although all three of these proteins are G-protein coupled receptors (GPCRs), activation of AVPR1A and AVPR1B stimulate
phospholipase C Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...
, while activation of AVPR2 stimulates adenylate cyclase. These three receptors for vasopressin have unique tissue distributions. AVPR1A are expressed in vascular smooth muscle cells, hepatocytes, platelets, brain cells, and uterus cells. AVPR1B are expressed in cells of the anterior pituitary and throughout the brain, especially in the pyramidal neurons of the hippocampal CA2 field. AVPR2 are expressed in the
kidney tubule The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ca ...
, predominantly in the
distal convoluted tubule The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule. Physiology It is partly responsible for the regulation of potassium, sodium, calcium, and pH. On its apical surface (lumen ...
and collecting ducts, in fetal
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
tissue and
lung cancer Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. Lung carcinomas derive from transformed, mali ...
, the last two being associated with
alternative splicing Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be i ...
. AVPR2 is also expressed in the liver where stimulation releases a variety of
clotting factor Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a thrombus, blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The m ...
s into the bloodstream. In the kidney, AVPR2's primary function is to respond to arginine vasopressin by stimulating mechanisms that concentrate the
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellul ...
and maintain
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
homeostasis In biology, homeostasis ( British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
in the organism. When the function of AVPR2 is lost, the disease
Nephrogenic Diabetes Insipidus Nephrogenic diabetes insipidus, also known as renal diabetes insipidus, is a form of diabetes insipidus primarily due to pathology of the kidney. This is in contrast to central or neurogenic diabetes insipidus, which is caused by insufficient le ...
(NDI) results.


Antagonists

Vasopressin receptor antagonist A vasopressin receptor antagonist (VRA) is an agent that interferes with action at the vasopressin receptors. Most commonly VRAs are used in the treatment of hyponatremia, especially in patients with congestive heart failure, liver cirrhosis or SIAD ...
s (VRAs) are drugs that block vasopressin receptors. Most commonly VRAs are used to treat hyponatremia caused by syndrome of inappropriate antidiuretic hormone secretion (SIADH),
congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...
(CHF) and
cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue rep ...
. Somatostatin is a competitive inhibitor. Inhibition by somatostatin of the vasopressin-stimulated adenylate cyclase in a kidney-derived line of cells grown in defined medium. FEBS Letters. https://doi.org/10.1016/0014-5793(84)80304-X Normally, when osmolality falls below its set point, plasma vasopressin levels become undetectable, and an aquaresis results. In SIADH, vasopressin release is not fully suppressed, despite hypotonicity. In
cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue rep ...
and CHF, impaired delivery of solute to the diluting sites or diminished glomerular filtration rate causes impairment of maximal water-excretory capacity, resulting in persistence of vasopressin release leading to water retention. Vasopressin receptor antagonists include the new class of "vaptan drugs" such as
conivaptan Conivaptan, sold under the brand name Vaprisol, is a non-peptide inhibitor of the receptor for anti-diuretic hormone, also called vasopressin. It was approved in 2004 for hyponatremia (low blood sodium levels). The compound was discovered by As ...
,
tolvaptan Tolvaptan, sold under the brand name Samsca among others, is an aquaretic drug that functions as a selective, competitive vasopressin receptor 2 (V2) antagonist used to treat hyponatremia (low blood sodium levels) associated with congestive he ...
,
mozavaptan Mozavaptan (INN Inns are generally establishments or buildings where travelers can seek lodging, and usually, food and drink. Inns are typically located in the country or along a highway; before the advent of motorized transportation they al ...
, lixivaptan, satavaptan etc.


References


External links

* * {{Oxytocin and vasopressin receptor modulators G protein-coupled receptors