Renin-Angiotensin System: How Peptides Set Blood Pressure
Blood Pressure Peptides
8 peptides
At least eight distinct angiotensin peptides have been identified in the renin-angiotensin system, each with different biological activity.
Patel et al., Biomedicine & Pharmacotherapy, 2017
Patel et al., Biomedicine & Pharmacotherapy, 2017
View as imageYour blood pressure at this moment is being set by a cascade of peptide hormones. The renin-angiotensin system (RAS) converts the liver protein angiotensinogen into a sequence of smaller peptides, each with different effects on blood vessels, kidneys, and the heart. Angiotensin II, the most potent product, constricts arteries and raises blood pressure. But a counter-regulatory arm, driven by the enzyme ACE2 and the peptide angiotensin-(1-7), pushes back in the opposite direction. The balance between these two arms determines your vascular state at any given second. This is the peptide system that ACE inhibitors block and that sacubitril/valsartan manipulates from the other side.
Key Takeaways
- The RAS produces at least eight bioactive peptides from a single precursor protein, angiotensinogen, each with distinct vascular and renal effects (Patel et al., Biomedicine & Pharmacotherapy, 2017)
- Angiotensin II raises blood pressure through direct vasoconstriction, aldosterone release, sodium retention, and sympathetic nervous system activation (Atlas, JMCP, 2007)
- ACE2 was discovered in 2000 as a homolog of ACE that converts angiotensin II into the vasodilatory peptide angiotensin-(1-7) (Donoghue et al., Circulation Research, 2000)
- Angiotensin-(1-7) opposes angiotensin II by triggering nitric oxide release and reducing inflammation via the Mas receptor (Chappell, Contributions to Nephrology, 2004)
- Angiotensin III carries 100% of angiotensin II's aldosterone-stimulating activity but only 40% of its vasoconstrictor potency (Padia and Carey, Peptides, 2013)
- Local tissue RAS systems operate independently in the brain, heart, kidneys, and blood vessels, with autocrine and paracrine functions beyond the circulating system (Patel et al., Biomedicine & Pharmacotherapy, 2017)
A 128-year-old discovery that keeps expanding
Robert Tigerstedt and Per Bergman first described renin in 1898 after injecting crude kidney extracts into rabbits and observing a sustained blood pressure rise. Their work was largely ignored for decades. It was not until the 1930s and 1940s that two independent groups, one in Argentina (Braun-Menendez) and one in the United States (Page and Helmer), simultaneously isolated the pressor substance produced by renin's action on plasma protein. They named it "hypertensin" and "angiotonin," respectively, and later agreed on the merged term "angiotensin."[3]
Basso and Terragno documented this history in 2001, noting that the parallel discovery in Buenos Aires and Cleveland reflected the global nature of hypertension research from its earliest days. The identification of ACE came in the 1950s, followed by the first ACE inhibitor (captopril) in 1981, which transformed the RAS from a physiological curiosity into one of the most targeted systems in cardiovascular medicine.[3]
Each decade has added complexity. The 1980s brought local tissue RAS. The 1990s identified angiotensin-(1-7) as biologically active. The 2000s delivered ACE2. The 2020s revealed alamandine derivatives. The system that looked simple in 1898 now contains at least eight peptides, four receptor types, multiple processing enzymes, and independent tissue-level subsystems.
How the classical RAS cascade works
The system starts in the liver. Hepatocytes constitutively produce angiotensinogen, a 452-amino-acid protein that circulates in the blood as an inactive precursor. The liver releases it continuously regardless of blood pressure status.[1]
The rate-limiting step is renin. Juxtaglomerular cells in the kidney's afferent arterioles store renin in granules and release it in response to four signals: a drop in renal perfusion pressure, reduced sodium chloride delivery at the macula densa, increased sympathetic nerve activity via beta-1 adrenergic receptors, and a decrease in negative feedback from circulating angiotensin II.[2]
Renin is technically a protease, not a peptide hormone, but its substrate and products are all peptides. It cleaves the first 10 amino acids from angiotensinogen to produce angiotensin I, a decapeptide with no significant biological activity on its own.[1]
Angiotensin-converting enzyme (ACE), located primarily on pulmonary endothelial cells, then removes two amino acids from angiotensin I's C-terminus to produce the octapeptide angiotensin II. This is the primary effector molecule of the classical RAS. The lungs are the major site of this conversion because the entire cardiac output passes through the pulmonary vasculature, giving ACE access to virtually all circulating angiotensin I.[2]
What angiotensin II does to your body
Angiotensin II is one of the most potent vasoconstrictors in human physiology. It acts through two main receptor types: AT1 and AT2. The AT1 receptor mediates nearly all of the blood-pressure-raising effects.[3]
Through AT1 receptors, angiotensin II triggers at least five parallel mechanisms to raise blood pressure:
Direct vasoconstriction. Angiotensin II contracts vascular smooth muscle in arterioles throughout the body. This increases systemic vascular resistance, the single largest determinant of diastolic blood pressure.[3]
Aldosterone secretion. Angiotensin II stimulates the adrenal cortex to release aldosterone, which acts on the distal nephron to increase sodium reabsorption and potassium excretion. More sodium retention means more water retention and higher blood volume.[2]
Vasopressin release. Angiotensin II stimulates the posterior pituitary to secrete antidiuretic hormone (ADH/vasopressin), which promotes water reabsorption in the collecting ducts.[1]
Sympathetic potentiation. Angiotensin II enhances norepinephrine release from sympathetic nerve terminals and inhibits its reuptake, amplifying the sympathetic contribution to vascular tone.[3]
Thirst stimulation. Acting on the subfornical organ in the brain, angiotensin II triggers thirst and sodium appetite, increasing fluid intake.[2]
The AT2 receptor generally opposes AT1. It promotes vasodilation, inhibits cell growth, and triggers anti-inflammatory pathways. AT2 is highly expressed in fetal tissue, declines after birth, and is re-expressed in pathological conditions like heart failure and tissue injury.[3]
Tsutamoto and colleagues showed in 2000 that blocking the AT1 receptor in patients with heart failure reduced circulating levels of tumor necrosis factor-alpha, interleukin-6, and soluble adhesion molecules. This demonstrated that angiotensin II drives inflammation beyond its direct hemodynamic effects.[4]
ACE2 and the counter-regulatory axis
For a century, the RAS was understood as a linear cascade that raised blood pressure. The discovery of ACE2 in 2000 changed that understanding. Donoghue and colleagues cloned a novel carboxypeptidase, homologous to ACE, that cleaved angiotensin I into the nonapeptide angiotensin-(1-9).[5]
ACE2 turned out to be more significant for what it does to angiotensin II. It removes a single amino acid from angiotensin II's C-terminus, converting the vasoconstrictor into the heptapeptide angiotensin-(1-7). This single amino acid removal flips the peptide's biological activity from vasoconstriction to vasodilation.[6]
Angiotensin-(1-7) acts through the Mas receptor to produce effects that directly oppose angiotensin II: it promotes vasodilation through nitric oxide release, inhibits vascular smooth muscle proliferation, reduces fibrosis, and exerts anti-inflammatory effects.[6]
Chappell's 2004 review of the renal RAS established that the balance between the ACE/angiotensin II/AT1 axis and the ACE2/angiotensin-(1-7)/Mas axis determines net vascular tone. In the kidney, angiotensin-(1-7) increases sodium excretion and water excretion, directly opposing the sodium-retaining effects of aldosterone triggered by angiotensin II.[7]
Patel and colleagues reviewed the ACE2/angiotensin-(1-7) axis in heart failure in 2016, showing that reduced ACE2 activity shifts the balance toward angiotensin II dominance, contributing to cardiac remodeling, fibrosis, and progressive dysfunction. In animal models, restoring ACE2 activity or administering angiotensin-(1-7) improved cardiac function and reduced fibrosis.[8]
This counter-regulatory pathway also became unexpectedly relevant during the COVID-19 pandemic. SARS-CoV-2 uses ACE2 as its cell entry receptor, and viral binding reduces ACE2 surface expression. The resulting loss of angiotensin-(1-7) production tilts the local RAS toward unchecked angiotensin II activity, contributing to the inflammatory lung injury characteristic of severe COVID-19.[8]
The other angiotensin peptides
The RAS produces far more than angiotensin I and II. At least six additional bioactive peptides have been identified, each with different receptor affinities and biological roles.[1]
Angiotensin III (angiotensin 2-8) is produced when aminopeptidase A removes angiotensin II's N-terminal amino acid. It carries 100% of angiotensin II's aldosterone-stimulating activity in the adrenal gland but only about 40% of its vasoconstrictor potency. Padia and Carey argued in their 2013 review that angiotensin III, not angiotensin II, may be the primary regulator of aldosterone secretion and renal sodium reabsorption in the kidney.[9]
Angiotensin IV (angiotensin 3-8) is a hexapeptide produced by further aminopeptidase cleavage. It binds the AT4 receptor, now identified as insulin-regulated aminopeptidase (IRAP). Angiotensin IV has been linked to cognitive function, with studies showing it enhances memory in animal models through mechanisms distinct from blood pressure regulation.[9]
Angiotensin-(1-9) is produced when ACE2 cleaves angiotensin I. It has cardioprotective effects, reducing cardiac hypertrophy and fibrosis through AT2 receptor activation.[5]
Alamandine is formed by decarboxylation of angiotensin-(1-7) and acts through the MrgD receptor. Santos and colleagues reported the identification of alamandine-(1-5) as the newest component of the RAS in 2026, expanding the system's known peptide repertoire further into territory that opposes vasoconstriction.[10]
Local tissue RAS: beyond the bloodstream
The classical description of the RAS as a circulating hormonal system is incomplete. Every major organ contains a local RAS that produces angiotensin peptides independently of circulating renin and angiotensinogen.[1]
The brain has its own complete RAS behind the blood-brain barrier. Angiotensin II produced locally in the brain regulates sympathetic outflow, thirst, vasopressin release, and blood pressure setpoints in the medulla oblongata and hypothalamus.[3]
The heart expresses all RAS components. Cardiac angiotensin II drives hypertrophy, fibrosis, and remodeling independently of its hemodynamic effects. This local production explains why ACE inhibitors improve cardiac outcomes beyond what blood pressure reduction alone would predict.[2]
The kidney has perhaps the highest local angiotensin II concentrations of any organ, with intrarenal levels exceeding plasma concentrations by 100- to 1000-fold. This local system directly controls sodium handling, glomerular filtration, and tubular reabsorption independently of the systemic circulation.[7]
The vasculature itself produces angiotensin II through ACE expressed on endothelial cells and through non-ACE pathways including chymase. Bernstein and colleagues showed in 2024 that ACE has nonclassical effects on myeloid immune cells, enhancing their antimicrobial function through mechanisms unrelated to angiotensin peptide production.[6]
These local RAS systems are why blood pressure drugs that target the RAS have effects far beyond hemodynamics. Food-derived ACE-inhibitory peptides from dairy and plant proteins also interact with this same enzymatic machinery, though at concentrations far below those achieved by pharmaceutical ACE inhibitors.
Why the RAS matters for peptide science
The RAS is arguably the most pharmacologically productive peptide system in medicine. Five major drug classes target it: ACE inhibitors, angiotensin receptor blockers (ARBs), direct renin inhibitors, aldosterone antagonists, and angiotensin receptor-neprilysin inhibitors (ARNIs).[3]
The discovery of the counter-regulatory ACE2/angiotensin-(1-7)/Mas axis opened new therapeutic possibilities. Recombinant ACE2, angiotensin-(1-7) analogs, and Mas receptor agonists are all under investigation. The ACE2 pathway is also the reason SARS-CoV-2 gains cell entry, which put a previously obscure enzyme at the center of pandemic research.[8]
Each class works at a different point in the cascade. ACE inhibitors prevent angiotensin II from being made. ARBs let it be made but block its receptor. Direct renin inhibitors stop the cascade at step one. This redundancy in drug targets reflects how many intervention points a peptide cascade offers compared to a simple receptor-ligand pair.[2]
The newest class, ARNIs, takes a different approach entirely. Rather than just blocking the harmful arm, sacubitril/valsartan simultaneously blocks AT1 receptors and inhibits neprilysin, the enzyme that degrades natriuretic peptides like BNP and ANP. This boosts the body's natural counter-pressure system while suppressing the pressure-raising arm. In the PARADIGM-HF trial, this dual approach reduced cardiovascular death and heart failure hospitalization by 20% compared to the ACE inhibitor enalapril alone.[8]
The system also illustrates a broader principle about peptide hormones: small changes in amino acid sequence produce dramatically different biological effects. Angiotensin II (8 amino acids) constricts vessels. Remove one amino acid to get angiotensin-(1-7), and the peptide dilates them instead. The difference between hypertension and vasodilation is a single amino acid.
The RAS intersects with natriuretic peptides at multiple points. ANP and BNP oppose angiotensin II by promoting sodium excretion and vasodilation. The drug sacubitril/valsartan exploits this intersection by simultaneously blocking angiotensin II (valsartan, an ARB) and boosting natriuretic peptides (sacubitril, a neprilysin inhibitor).
The Bottom Line
The renin-angiotensin system is a peptide cascade that produces at least eight bioactive fragments from a single precursor protein. The classical arm, centered on angiotensin II and the AT1 receptor, raises blood pressure through vasoconstriction, sodium retention, and sympathetic activation. The counter-regulatory arm, centered on ACE2, angiotensin-(1-7), and the Mas receptor, opposes these effects through vasodilation and anti-inflammatory signaling. Local tissue RAS systems in the brain, heart, kidneys, and vasculature operate independently of the circulating system. Five drug classes now target this peptide network, and newer therapies aim to boost the protective arm rather than simply blocking the harmful one.