ANGIOTENSIN II, HUMAN

Discovery

Angiotensin II is the active peptide hormone of the reninangiotensin system (RAS) with broad functions, including a vasopressor effect and thirst stimulation. It is a drug target for hypertension and renal diseases. In 1940, two groups of researchers separately discovered a potent vasoconstrictor by incubating plasma with renin; the substance was named both “angiotonin” and “hypertensin.” In 1958, they agreed to rename it “angiotensin” (angio=blood vessel; tensin=tension).

Structure

Ang II is a linear peptide with no known secondary modification. Ang II is produced by the subsequent cleavage of angiotensinogen (AGT) by renin and angiotensin I (Ang I) by ACE (See Renin Angiotensin System). Mr. 1046 of Ang II in humans. Freely soluble in water.

Gene, mRNA, and mRNA

AGT is located on chromosome 1q42.2 in humans. AGT belongs to the SERPIN family A, member 8. AGT protein sequences are highly variable but the functional domains (Ang I) are relatively conserved among vertebrates. Ang I sequences were identified by the incubation of a renin source (kidney extract) and an angiotensinogen source (plasma). Lamprey Ang I with sequence NRVYVHPFTL was first sequenced using peptide purification. However, the lamprey genome data suggested a different Ang I sequence, and was later confirmed as the native AGT. The purified teleost-type Ang I produced in the buccal gland was suggested to be involved in endocrine mimicry to reduce host immunorejection.

Agonist

A nonpeptide ligand, L-162,313 was shown to bind to AT1A, AT1B, and the AT2 receptor and act as an agonist on AT1A and AT1B receptors in mice (34.9 and 23.3% of the maximum response of Ang II, respectively). Early studies used CGP42112A as the agonist for the AT2 receptor but compound 21, with little affinity for the AT1 receptor, was recently developed as a specific agonist of the AT2 receptor in humans.

Antagonist

Saralasin ([Sar1 ], [Ala8 ]-Ang II) is a partial agonist of angiotensin II receptors, though it is commonly mistaken as a competitive antagonist. Antagonists including losartan, irbesartan, olmesartan, candesartan, and valsartan are commonly used clinically as AT1 blockers. Two AT2 receptor antagonists, PD123177 (discontinued) and PD123319 (available), were developed to inhibit AT2 activities.

Biological functions

Ang II/AT1 axis mediates vasoconstriction, thirst, release of vasopressin and aldosterone, renal sodium reabsorption, fibrosis, inflammation, angiogenesis, vascular aging, and atherosclerosis. Ang II-induced effects included blood pressure control; drinking; adrenergic stimulation; modulation of the ion pump and transporter activities in the gill, kidney, and intestine in fish; control of the filtering nephron population in fish; and regulation of ventral skin absorption in amphibians. The injection of Ang II significantly increased ventral skin drinking in the frog. Lamprey Ang II is a vasodepressor instead of a vasopressor when injected intraarterially. The intracerebroventricular (ICV) injection of Ang II into the trout increased the systemic blood pressure, heart rate, and ventilation rate. The ICV injection of Ang II elicits tachycardia in contrast to bradycardia when injected peripherally. Central Ang II injection also inhibits the vagal-mediated baro-reflex, indicating that brain RAS is involved in the heart rate control.
The AT2 receptor is mostly embryonic. The expression decreases in adults and is confined in certain tissues such as the kidney. The effects of AT2 are often antagonistic to AT1, and activation of the AT2 receptor usually indicates a pathophysiological condition of AT1-mediated action with potential harmful consequences. AT2 is abundantly expressed in the spleen of the adult eel, which suggests an immune-related function.

Description

It is known that tumor tissues including metastatic lymph nodes are composed of newly growing vessels which lack blood flow autoregulation and are influenced only secondarily by the responding somatic vessels. Human angiotensin II (AT II). a vasopressor, was introduced in Japan to improve the efficacy of systemic chemotherapy. In patients with various advanced cancers, i.v. infusion of AT II to achieve a mean blood pressure of 1.5 times of baseline (but not over 150 mm Hg) followed by a bolus injection of conventional cytotoxic agents increases blood flow 5-7 fold in tumor tissues and therefore, increases drug delivery to the target tissue resulting in enhanced chemotherapeutic effects. This induced-hypertension chemotherapy regimen can be performed safely with minimal side effects.

Description

Angiotensin II is a peptide hormone known best as a vasoconstrictor with central roles in chronic hypertension, heart failure, and stroke. It is an octapeptide typically generated by the removal of two residues from angiotensin I by angiotensin-converting enzyme (ACE). Angiotensin II is a ligand for at least two distinct receptors, AT₁ and AT₂, each evoking distinct signaling pathways and physiological responses. The development of antagonists for specific angiotensin II receptor subtypes represents a valuable alternative to ACE inhibitors.

Originator

Toa Eiyo (Japan)

Uses

Angiotensin II is a peptide hormone known best as a vasoconstrictor with central roles in chronic hypertension, heart failure, and stroke. It is an octapeptide typically generated by the removal of two residues from angiotensin I by angiotensin-converting enzyme (ACE). Angiotensin II is a ligand for at least two distinct receptors, AT1 and AT2, each evoking distinct signaling pathways and physiological responses. The development of antagonists for specific angiotensin II receptor subtypes represents a valuable alternative to ACE inhibitors.

Uses

A peptide involved in the regulation of blood pressure

Uses

Cardiopulmonary resuscitation - not yet an approved application

Definition

ChEBI: Ile(5)-angiotensin II is an angiotensin II that acts on the central nervous system (PDB entry: 1N9V). It has a role as a human metabolite. It is a tautomer of an Ile(5)-angiotensin II dizwitterion.

brand name

Delivert

General Description

Functions in blood pressure maintenance. Stimulates the release of aldosterone from the adrenal gland. Has strong vasoconstrictive effects. Increases the entry of Ca²⁺ in heart muscle via voltage-sensitive channels and activates myosin light chain kinase. Activates JAK2 in smooth muscle cells. Activates p125^FAK and a cytosolic 115-120 kDa calcium-dependent tyrosine kinase in rat epithelial cells. Also activates pp60c-src in vascular smooth muscle cells. Inhibits adenylate cyclase activity in spontaneously hypertensive rats.

Biochem/physiol Actions

Product does not compete with ATP.

Clinical Use

Renin antagonists, ACE inhibitors, and AT1 receptor blockers have been used, in singular or multiple blockade, to treat hypertension and other RAS-related diseases. High levels of Ang II are often related to hypertension, renal failure, and cardiac fibrosis.

in vitro

Most of the known actions of Angiotensin II (Ang II) are mediated by AT 1 receptors, the AT 2 receptor contributes to the regulation of blood pressure and renal function. Angiotensin II raises blood pressure (BP) by a number of actions, the most important ones being vasoconstriction, sympathetic nervous stimulation, increased aldosterone biosynthesis and renal actions. Other Angiotensin II actions include induction of growth, cell migration, and mitosis of vascular smooth muscle cells, increased synthesis of collagen type I and III in fibroblasts, leading to thickening of the vascular wall and myocardium, and fibrosis. These actions are mediated by type 1 Ang II receptors (AT 1 ). At the cellular level, responsiveness to Angiotensin II is conferred by the expression of the two classes of angiotensin receptors (AT 1 and AT 2 ). The effects of Angiotensin II to increase blood pressure are mediated by AT1 receptors.

in vivo

To distinguish the AT 1 receptor population that is critical for the pathogenesis of hypertension, osmotic minipumps are implanted s.c. into each animal to infuse Angiotensin II (1,000 ng/kg/min) continuously for 4 weeks. Angiotensin II causes hypertension by activating AT 1 receptors in the kidney promoting sodium reabsorption.

storage

-20°C (desiccate)