Angiotensin

Angiotensinogen (serpin peptidase inhibitor, clade A, member 8)
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 1N9U, 1N9V, 2JP8, 2WXW, 2X0B, 3CK0, 3WOO, 3WOR, 4AA1, 4APH, 4FYS
Identifiers
Symbols	AGT ; ANHU; SERPINA8
External IDs	OMIM: 106150 MGI: 87963 HomoloGene: 14 GeneCards: AGT Gene
Gene ontology Molecular function • serine-type endopeptidase inhibitor activity • hormone activity • protein binding • growth factor activity • superoxide-generating NADPH oxidase activator activity • sodium channel regulator activity • type 1 angiotensin receptor binding • type 2 angiotensin receptor binding Cellular component • extracellular region • extracellular space • cytoplasm • extracellular exosome • blood microparticle Biological process • ovarian follicle rupture • regulation of cell growth • blood vessel development • branching involved in ureteric bud morphogenesis • positive regulation of cytokine production • kidney development • blood vessel remodeling • angiotensin mediated vasoconstriction involved in regulation of systemic arterial blood pressure • renal response to blood flow involved in circulatory renin-angiotensin regulation of systemic arterial blood pressure • angiotensin maturation • regulation of blood volume by renin-angiotensin • renin-angiotensin regulation of aldosterone production • regulation of renal output by angiotensin • regulation of heart rate • regulation of blood vessel size by renin-angiotensin • renal system process • angiotensin-mediated drinking behavior • positive regulation of extracellular matrix constituent secretion • cellular sodium ion homeostasis • cell-matrix adhesion • G-protein coupled receptor signaling pathway • G-protein coupled receptor signaling pathway coupled to cGMP nucleotide second messenger • phospholipase C-activating G-protein coupled receptor signaling pathway • activation of phospholipase C activity • activation of NF-kappaB-inducing kinase activity • nitric oxide mediated signal transduction • cell-cell signaling • female pregnancy • aging • excretion • establishment of blood-nerve barrier • regulation of blood pressure • negative regulation of cell proliferation • response to cold • response to salt stress • positive regulation of activation of JAK2 kinase activity • positive regulation of endothelial cell migration • positive regulation of cardiac muscle hypertrophy • positive regulation of macrophage derived foam cell differentiation • positive regulation of cholesterol esterification • negative regulation of endopeptidase activity • regulation of norepinephrine secretion • positive regulation of phosphatidylinositol 3-kinase signaling • artery smooth muscle contraction • response to muscle activity involved in regulation of muscle adaptation • negative regulation of angiogenesis • regulation of vasoconstriction • extracellular matrix organization • negative regulation of cell growth • peristalsis • positive regulation of cellular protein metabolic process • positive regulation of superoxide anion generation • positive regulation of peptidyl-serine phosphorylation • positive regulation of NAD(P)H oxidase activity • negative regulation of tissue remodeling • low-density lipoprotein particle remodeling • catenin import into nucleus • regulation of renal sodium excretion • positive regulation of renal sodium excretion • positive regulation of multicellular organism growth • regulation of cell proliferation • vasodilation • positive regulation of MAPK cascade • negative regulation of neuron apoptotic process • cellular lipid metabolic process • cellular protein metabolic process • small molecule metabolic process • positive regulation of nitric oxide biosynthetic process • positive regulation of fatty acid biosynthetic process • positive regulation of epidermal growth factor receptor signaling pathway • positive regulation of transcription, DNA-templated • positive regulation of vasodilation • positive regulation of organ growth • astrocyte activation • fibroblast proliferation • positive regulation of fibroblast proliferation • regulation of long-term neuronal synaptic plasticity • smooth muscle cell proliferation • cytokine secretion • positive regulation of inflammatory response • positive regulation of peptidyl-tyrosine phosphorylation • positive regulation of NF-kappaB transcription factor activity • smooth muscle cell differentiation • negative regulation of neurotrophin TRK receptor signaling pathway • stress-activated MAPK cascade • regulation of calcium ion transport • regulation of transmission of nerve impulse • cell growth involved in cardiac muscle cell development • positive regulation of protein tyrosine kinase activity • ERK1 and ERK2 cascade • uterine smooth muscle contraction • cellular response to mechanical stimulus • positive regulation of branching involved in ureteric bud morphogenesis • positive regulation of protein kinase C activity • regulation of extracellular matrix assembly • positive regulation of membrane hyperpolarization • positive regulation of gap junction assembly • regulation of cardiac conduction • positive regulation of reactive oxygen species metabolic process • negative regulation of sodium ion transmembrane transporter activity • positive regulation of extrinsic apoptotic signaling pathway Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	183	11606
Ensembl	ENSG00000135744	ENSMUSG00000031980
UniProt	P01019	n/a
RefSeq (mRNA)	NM_000029	NM_007428
RefSeq (protein)	NP_000020	NP_031454
Location (UCSC)	Chr 1: 230.7 – 230.71 Mb	Chr 8: 124.56 – 124.57 Mb
PubMed search	[1]	[2]

Angiotensin is a peptide hormone that causes vasoconstriction and a subsequent increase in blood pressure. It is part of the renin-angiotensin system, which is a major target for drugs that lower blood pressure. Angiotensin also stimulates the release of aldosterone, another hormone, from the adrenal cortex. Aldosterone promotes sodium retention in the distal nephron, in the kidney, which also drives blood pressure up.

Angiotensin is an oligopeptide and is a hormone and a powerful dipsogen. It is derived from the precursor molecule angiotensinogen, a serum globulin produced in the liver. It plays an important role in the renin-angiotensin system. Angiotensin was independently isolated in Indianapolis and Argentina in the late 1930s (as 'angiotonin' and 'hypertensin', respectively) and subsequently characterised and synthesized by groups at the Cleveland Clinic and Ciba laboratories in Basel, Switzerland.

Precursor, and types of angiotensin

Angiotensinogen

Angiotensinogen is an α-2-globulin produced constitutively and released into the circulation mainly by the liver. It is a member of the serpin family, although it is not known to inhibit other enzymes, unlike most serpins. Plasma angiotensinogen levels are increased by plasma corticosteroid, estrogen, thyroid hormone, and angiotensin II levels.

Angiotensinogen is also known as renin substrate. Human angiotensinogen is 453 amino acids long, but other species have angiotensinogen of varying sizes. The first 12 amino acids are the most important for activity.

Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-...

Angiotensin I

Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu | Val-Ile-...

Renin–angiotensin–aldosterone system

Angiotensin I (CAS# 11128-99-7) is formed by the action of renin on angiotensinogen. Renin cleaves the peptide bond between the leucine (Leu) and valine (Val) residues on angiotensinogen, creating the ten-amino acid peptide (des-Asp) angiotensin I. Renin is produced in the kidneys in response to renal sympathetic activity, decreased intrarenal blood pressure (<90mmHg systolic blood pressure ) at the juxtaglomerular cells, or decreased delivery of Na+ and Cl- to the macula densa. If less Na+ is sensed by the macula densa, renin release by juxtaglomerular cells is increased.

Angiotensin I appears to have no biological activity and exists solely as a precursor to angiotensin II.

Angiotensin II

Asp-Arg-Val-Tyr-Ile-His-Pro-Phe | His-Leu

Angiotensin I is converted to angiotensin II (AII) through removal of two C-terminal residues by the enzyme angiotensin-converting enzyme (ACE), primarily through ACE within the lung (but also present in endothelial cells and kidney epithelial cells). ACE found in other tissues of the body has no physiological role (ACE has a high density in the lung, but activation here promotes no vasoconstriction, angiotensin II is below physiological levels of action). Angiotensin II acts as an endocrine, autocrine/paracrine, and intracrine hormone.

ACE is a target for inactivation by ACE inhibitor drugs, which decrease the rate of Angiotensin II production. Angiotensin II increases blood pressure by stimulating the Gq protein in vascular smooth muscle cells (which in turn activates an IP3-dependent mechanism leading to a rise in intracellular calcium levels and ultimately causing contraction). In addition, angiotensin II acts at the Na/H exchanger in the proximal tubules of the kidney to stimulate Na reabsorption and H excretion which is coupled to bicarbonate reabsorption. This ultimately results in an increase in blood volume, pressure, and pH. Hence, ACE inhibitors are major anti-hypertensive drugs.

Other cleavage products of ACE, seven or 9 amino acids long, are also known; they have differential affinity for angiotensin receptors, although their exact role is still unclear. The action of AII itself is targeted by angiotensin II receptor antagonists, which directly block angiotensin II AT₁ receptors.

Angiotensin II is degraded to angiotensin III by angiotensinases located in red blood cells and the vascular beds of most tissues. It has a half-life in circulation of around 30 seconds, whereas, in tissue, it may be as long as 15–30 minutes.

Angiotensin III

Asp | Arg-Val-Tyr-Ile-His-Pro-Phe

Angiotensin III has 40% of the pressor activity of angiotensin II, but 100% of the aldosterone-producing activity. Increases mean arterial pressure.

Angiotensin IV

Arg | Val-Tyr-Ile-His-Pro-Phe

Angiotensin IV is a hexapeptide that, like angiotensin III, has some lesser activity.

Effects

See also Renin-angiotensin system#Effects

Angiotensins II, III and IV have a number of effects throughout the body:

Adipic

Angiotensins "modulate fat mass expansion through upregulation of adipose tissue lipogenesis ... and downregulation of lipolysis "

Cardiovascular

They are potent direct vasoconstrictors, constricting arteries and veins and increasing blood pressure. This effect is achieved through activation of the GCPR AT1, which signals through a Gq protein to activate Phospholipase C, and subsequently increase intracellular calcium.

Angiotensin II has prothrombotic potential through adhesion and aggregation of platelets and stimulation of PAI-1 and PAI-2.

When cardiac cell growth is stimulated, a local (autocrine-paracrine) renin-angiotensin system is activated in the cardiac myocyte, which stimulates cardiac cell growth through protein kinase C. The same system can be activated in smooth muscle cells in conditions of hypertension, atherosclerosis, or endothelial damage. Angiotensin II is the most important Gq stimulator of the heart during hypertrophy, compared to endothelin-1 and α1 adrenoreceptors.

Neural

Angiotensin II increases thirst sensation (dipsogen) through the subfornical organ of the brain, decreases the response of the baroreceptor reflex, and increases the desire for salt. It increases secretion of ADH in the posterior pituitary and secretion of ACTH in the anterior pituitary. It also potentiates the release of norepinephrine by direct action on postganglionic sympathetic fibers.

Adrenal

Angiotensin II acts on the adrenal cortex, causing it to release aldosterone, a hormone that causes the kidneys to retain sodium and lose potassium. Elevated plasma angiotensin II levels are responsible for the elevated aldosterone levels present during the luteal phase of the menstrual cycle.

Renal

Angiotensin II has a direct effect on the proximal tubules to increase Na⁺ reabsorption. It has a complex and variable effect on glomerular filtration and renal blood flow depending on the setting. Increases in systemic blood pressure will maintain renal perfusion pressure; however, constriction of the afferent and efferent glomerular arterioles will tend to restrict renal blood flow. The effect on the efferent arteriolar resistance is, however, markedly greater, in part due to its smaller basal diameter; this tends to increase glomerular capillary hydrostatic pressure and maintain glomerular filtration rate. A number of other mechanisms can affect renal blood flow and GFR. High concentrations of Angiotensin II can constrict the glomerular mesangium, reducing the area for glomerular filtration. Angiotensin II is a sensitizer to tubuloglomerular feedback, preventing an excessive rise in GFR. Angiotensin II causes the local release of prostaglandins, which, in turn, antagonize renal vasoconstriction. The net effect of these competing mechanisms on glomerular filtration will vary with the physiological and pharmacological environment.

Direct Renal effects of angiotensin II (not including aldosterone release)

Target	Action	Mechanism
renal artery & afferent arterioles	vasoconstriction (weaker)	VDCCs → Ca2+ influx
efferent arteriole	vasoconstriction (stronger)	(probably) activate Angiotensin receptor 1 → Activation of Gq → ↑PLC activity → ↑IP3 and DAG → activation of IP3 receptor in SR → ↑intracellular Ca2+
mesangial cells	contraction → ↓filtration area	activation of Gq → ↑PLC activity → ↑IP3 and DAG → activation of IP3 receptor in SR → ↑intracellular Ca2+ VDCCs → Ca2+ influx
proximal tubule	increased Na+ reabsorption	adjustment of Starling forces in peritubular capillaries to favour increased reabsorption efferent and afferent arteriole contraction → decreased hydrostatic pressure in peritubular capillaries efferent arteriole contraction → increased filtration fraction → increased colloid osmotic pressure in peritubular capillaries increased sodium–hydrogen antiporter activity
tubuloglomerular feedback	increased sensitivity	increase in afferent arteriole responsiveness to signals from macula densa
medullary blood flow	reduction

See also

• ACE inhibitor
• Angiotensin receptor
• Angiotensin II receptor antagonist
• Captopril
• Renin inhibitor

Further reading

• Brenner & Rector's The Kidney, 7th ed., Saunders, 2004.
• Mosby's Medical Dictionary, 3rd Ed., CV Mosby Company, 1990.
• Review of Medical Physiology, 20th Ed., William F. Ganong, McGraw-Hill, 2001.
• Clinical Physiology of Acid-Base and Electrolyte Disorders, 5th ed., Burton David Rose & Theodore W. Post McGraw-Hill, 2001

External links

• The MEROPS online database for peptidases and their inhibitors: I04.953
• Angiotensins at the US National Library of Medicine Medical Subject Headings (MeSH)