Endothelin: The Most Potent Vasoconstrictor

Cardiovascular Peptides

10x more potent

Endothelin-1 constricts blood vessels with roughly ten times the potency of angiotensin II, making it the strongest vasoconstrictor the human body produces.

Yanagisawa et al., Nature, 1988

Yanagisawa et al., Nature, 1988

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In 1988, Masashi Yanagisawa and colleagues at the University of Tsukuba isolated a 21-amino-acid peptide from the culture medium of porcine aortic endothelial cells. When injected into rats, it produced a sustained blood pressure increase that lasted over an hour, far outlasting any known vasoconstrictor.^[1] They named it endothelin. Within a decade, this single discovery generated over 10,000 published studies and a new class of drugs. For a broader view of how this peptide fits alongside other cardiovascular regulators, see our pillar article on adrenomedullin and cardiovascular peptides. Endothelin occupies the opposite end of the vascular spectrum from the vasodilators; where adrenomedullin relaxes blood vessels, endothelin clamps them shut with a force the body reserves for emergencies.

Discovery: From Cell Culture to Cardiovascular Revolution

Yanagisawa's 1988 paper in Nature described the isolation, sequencing, and cloning of a peptide that was approximately 100 times more potent than norepinephrine at constricting isolated porcine coronary artery strips.^[1] Endothelin's amino acid sequence revealed an unusual feature: two disulfide bonds creating a compact, bicyclic structure resembling the sarafotoxins, a group of snake venom toxins from the Israeli burrowing asp. This structural similarity to a lethal venom underscored the peptide's potency.

The discovery was electrifying because it identified the vascular endothelium (the single-cell layer lining blood vessels) as the source of the most powerful vasoconstrictor the body produces. Before 1988, the endothelium was considered a passive barrier. Endothelin, along with the earlier discovery of nitric oxide, redefined endothelial cells as active regulators of vascular tone.

Within a year, Inoue et al. (1989) cloned the genes encoding three distinct endothelin isoforms from a human genomic library.^[2] ET-1, the original peptide, differs from ET-2 at two amino acid positions and from ET-3 at six positions. All three produced vasoconstriction and blood pressure elevation when injected, but their potency and receptor binding profiles varied considerably, suggesting distinct physiological roles for each isoform.

Structure and Biosynthesis

Endothelin-1 is produced through a two-step proteolytic process. The gene encodes a 212-amino-acid precursor called preproendothelin-1. Signal peptidases remove the signal sequence to yield proendothelin-1, which is then cleaved by furin-like proteases into big endothelin-1, a 38-amino-acid intermediate. The final step, conversion of big endothelin-1 to the mature 21-amino-acid ET-1, is catalyzed by endothelin-converting enzyme-1 (ECE-1), a membrane-bound metalloprotease.^[3]

This two-step activation is not just biochemistry; it is a control mechanism. Big endothelin-1 has less than 1% of the vasoconstrictor activity of mature ET-1. The body keeps a large reservoir of the inactive precursor and uses ECE-1 as a gatekeeper, allowing rapid local activation without systemic flooding.

ET-1 production is stimulated by angiotensin II, thrombin, transforming growth factor-beta, hypoxia, and shear stress on the vascular wall. It is inhibited by nitric oxide, prostacyclin, and atrial natriuretic peptide. This regulatory network places endothelin at the intersection of virtually every major cardiovascular signaling pathway. ET-1 levels in healthy human plasma are extremely low (0.3 to 3 picograms per milliliter), reflecting the fact that most ET-1 acts locally and is cleared rapidly by the lungs.^[3]

The Two Receptor System: ETA and ETB

Endothelin signals through two G-protein coupled receptors with opposing vascular effects. The ETA receptor, predominantly expressed on vascular smooth muscle cells, mediates vasoconstriction, cell proliferation, inflammation, and fibrosis. The ETB receptor, predominantly expressed on endothelial cells, triggers the release of nitric oxide and prostacyclin, producing vasodilation. ETB receptors also function as clearance receptors, removing ET-1 from the circulation.^[3]

This dual-receptor system creates a built-in counterbalance. Under normal conditions, the vasodilatory ETB pathway helps keep the constrictive ETA pathway in check. In disease states, the balance shifts. Endothelial damage reduces ETB-mediated nitric oxide release while ETA-mediated constriction remains intact or increases, tipping the system toward sustained vasoconstriction.

The receptor selectivity of the three endothelin isoforms differs in an important way. ET-1 and ET-2 bind ETA and ETB with roughly equal affinity. ET-3, however, has markedly lower affinity for ETA and binds preferentially to ETB.^[2] This selectivity influences the pharmacological strategies used to target the endothelin system.

Endothelin in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) was the first disease where the endothelin system became a validated drug target. Patients with PAH have elevated ET-1 levels in plasma and lung tissue, and ET-1 overexpression drives the vasoconstriction, smooth muscle proliferation, and fibrosis that progressively narrow pulmonary arteries.

Channick et al. (2001) conducted the first randomized, placebo-controlled trial of bosentan, a dual ETA/ETB receptor antagonist, in 32 patients with PAH. Over 12 weeks, bosentan improved exercise capacity (six-minute walking distance) by 70 meters compared to a 6-meter decline in the placebo group.^[5]

The larger confirmatory trial by Rubin et al. (2002), published in the New England Journal of Medicine, randomized 213 patients with PAH to bosentan or placebo for 16 weeks. Bosentan improved six-minute walking distance by 44 meters over placebo, improved WHO functional class, reduced the Borg dyspnea index, and increased the time to clinical worsening.^[6] This trial led to FDA approval of bosentan (Tracleer) in 2001, the first oral treatment for PAH and the first drug to exploit endothelin receptor antagonism therapeutically.

Since then, three additional endothelin receptor antagonists have received FDA approval: ambrisentan (Letairis, 2007), a selective ETA antagonist; macitentan (Opsumit, 2013), a dual antagonist with improved tissue penetration; and aprocitentan (Tryvio, 2024), approved for resistant hypertension. Macitentan reduced the composite endpoint of morbidity and mortality by 45% versus placebo in the SERAPHIN trial, the longest randomized trial in PAH history (median treatment duration 115 weeks).^[4]

Wu et al. (2025) demonstrated that combining tadalafil with endothelin receptor antagonists in connective tissue disease-associated PAH produced additive improvements in pulmonary vascular resistance and exercise capacity, supporting the concept that targeting multiple pathways simultaneously yields better outcomes than monotherapy.^[10]

Endothelin in Heart Failure

Circulating ET-1 levels rise in proportion to heart failure severity. Kinugawa et al. (2003) measured plasma ET-1 in 114 patients with chronic heart failure and found that ET-1 levels increased progressively across NYHA functional classes I through IV. Patients in the highest ET-1 quartile had markedly worse cardiac index and higher pulmonary capillary wedge pressure.^[7]

Daggubati et al. (1997) examined ET-1 alongside other neurohormonal markers in a cohort of elderly patients with heart failure and found that ET-1 elevation correlated with disease severity independently of natriuretic peptides. The combination of elevated ET-1 and natriuretic peptides provided stronger prognostic information than either marker alone.^[8]

Despite the clear association between elevated ET-1 and heart failure, clinical trials of endothelin receptor antagonists in heart failure have been disappointing. Bosentan increased hepatotoxicity risk and fluid retention in heart failure patients, and trials were stopped early due to worsening symptoms. The ET system appears to play a compensatory role in heart failure, maintaining blood pressure and organ perfusion, so blocking it systemically causes harm. This is a sobering reminder that elevated levels of a biomarker do not automatically validate it as a drug target in every disease context.

Endothelin Beyond Blood Vessels

The endothelin system extends well beyond vascular regulation. ET-1 is expressed in the brain, kidneys, lungs, liver, and gastrointestinal tract. Rosenthal and Fromm (2011) reviewed the role of endothelin in glaucoma, where ET-1 constricts the blood vessels supplying the optic nerve head and directly promotes retinal ganglion cell death through ETA and ETB receptor signaling.^[9] For a detailed examination of this topic, see our article on endothelin and glaucoma.

Wang et al. (2025) found that ETA receptors on nociceptive sensory neurons are essential for persistent mechanical pain in chronic pancreatitis, revealing endothelin as a pain mediator that acts directly on nerve fibers rather than through vascular effects alone.^[11]

In the kidney, ET-1 produced by collecting duct cells regulates sodium and water excretion. ETB receptors in the kidney promote natriuresis (sodium excretion), and their blockade leads to sodium retention and hypertension. This renal biology explains why selective ETA antagonists like ambrisentan cause less fluid retention than dual ETA/ETB antagonists like bosentan.^[3]

ET-1 also drives fibrosis in the liver, lungs, and kidneys. Chronic ET-1 signaling through ETA activates hepatic stellate cells (the key fibrogenic cells in the liver), promotes collagen deposition in pulmonary tissue, and contributes to renal interstitial fibrosis. These pro-fibrotic effects are distinct from vasoconstriction and are under investigation as therapeutic targets in fibrotic diseases.^[4]

The Three Isoforms: ET-1, ET-2, and ET-3

ET-1 dominates the research literature, but the other two isoforms have distinct biology. ET-2, which differs from ET-1 at only two amino acid positions, was originally identified in the intestine and kidney. It is the least studied isoform, and its precise physiological role remains unclear, though recent work suggests it may function as a local regulator of ovarian and intestinal blood flow.^[4]

ET-3 differs from ET-1 at six positions and has a markedly different receptor profile, binding ETB with much higher affinity than ETA. This selectivity is biologically important. ET-3 plays a critical role in embryonic development, particularly in neural crest cell migration. Mutations in the ET-3 gene or the ETB receptor gene cause Hirschsprung disease, a congenital disorder where nerve cells fail to develop in portions of the intestine, and Waardenburg syndrome type IV, which combines Hirschsprung disease with hearing loss and pigmentation abnormalities.^[3] These developmental roles of ET-3 are entirely distinct from the vascular constriction that defines ET-1, illustrating how the same peptide family can serve radically different functions depending on the isoform and the tissue context.

Relationship to Other Cardiovascular Peptides

Endothelin does not act in isolation. It exists in a tightly regulated network with other vasoactive peptides. Angiotensin II stimulates ET-1 production, and ET-1 in turn amplifies angiotensin II signaling, creating a positive feedback loop that drives hypertension when uncontrolled. Bradykinin and nitric oxide counterbalance endothelin by promoting vasodilation. Apelin, a newer cardiovascular peptide, opposes angiotensin II and indirectly modulates endothelin signaling. Adrenomedullin, the most potent endogenous vasodilator peptide, functionally opposes endothelin in many vascular beds, and urotensin II shares some vasoconstrictor properties with endothelin in certain vascular territories.

This network architecture means that drugs targeting one peptide inevitably affect others. ACE inhibitors lower both angiotensin II and ET-1 levels. ANP inhibits ET-1 secretion. Understanding these interactions is essential for designing rational combination therapies, such as the dual angiotensin/endothelin receptor antagonist sparsentan, which received full FDA approval in 2024 for IgA nephropathy.

Current Limitations and Open Questions

Several important gaps remain in the understanding of endothelin biology. The roles of ET-2 and ET-3 are poorly characterized compared to ET-1. No selective ETA agonist has ever been discovered, which limits the ability to study ETA-mediated signaling in isolation.^[3]

The failure of endothelin receptor antagonists in heart failure remains incompletely explained. Whether this reflects compensatory signaling, fluid retention from ETB blockade, hepatotoxicity, or the wrong patient selection is still debated.

Endothelin's role in cancer is an active area of investigation. ET-1 signaling promotes tumor angiogenesis, cell survival, and metastasis in ovarian, prostate, and colorectal cancers. Early clinical trials of endothelin receptor antagonists in cancer have not produced clear survival benefits, though patient selection and combination strategies continue to evolve.

The newest frontier is the development of biased agonists and antagonists that selectively activate or block specific signaling pathways downstream of endothelin receptors, rather than blocking all receptor activity. This approach could preserve beneficial ETB-mediated clearance while blocking pathological ETA-mediated constriction and fibrosis.^[4]

The Bottom Line

Endothelin-1, discovered in 1988, is the most potent vasoconstrictor peptide the human body produces. Its biology spans vascular regulation, organ fibrosis, pain signaling, and neuroprotection. Four FDA-approved endothelin receptor antagonists have transformed the treatment of pulmonary arterial hypertension, and newer agents are extending the therapeutic reach to resistant hypertension and kidney disease. The system's complexity, with dual receptors producing opposing effects and interactions with virtually every other cardiovascular peptide pathway, means that targeting endothelin remains both clinically powerful and biologically challenging.

Frequently Asked Questions

What is endothelin and what does it do?

Endothelin is a family of three 21-amino-acid peptides (ET-1, ET-2, ET-3) produced primarily by vascular endothelial cells. ET-1, the most studied isoform, is the strongest vasoconstrictor the body makes, roughly 10 times more potent than angiotensin II. It regulates blood vessel tone, blood pressure, and organ blood flow. ET-1 also promotes cell proliferation, inflammation, and fibrosis when chronically elevated, contributing to diseases including pulmonary arterial hypertension, heart failure, and chronic kidney disease (Davenport et al., Pharmacological Reviews, 2016).

What causes high endothelin levels?

Elevated ET-1 levels result from endothelial cell activation by angiotensin II, thrombin, hypoxia, oxidative stress, and inflammatory cytokines. Conditions associated with chronically high ET-1 include pulmonary arterial hypertension, heart failure, chronic kidney disease, atherosclerosis, and diabetes. Plasma ET-1 in healthy adults ranges from 0.3 to 3 picograms per milliliter; levels rise proportionally with disease severity in heart failure, correlating with NYHA functional class (Kinugawa et al., J Cardiac Failure, 2003).

What drugs block endothelin receptors?

Four endothelin receptor antagonists (ERAs) have FDA approval. Bosentan (Tracleer, approved 2001) and macitentan (Opsumit, 2013) block both ETA and ETB receptors. Ambrisentan (Letairis, 2007) selectively blocks ETA. Aprocitentan (Tryvio, 2024) is a dual antagonist approved for resistant hypertension. In the pivotal NEJM trial, bosentan improved six-minute walking distance by 44 meters versus placebo in PAH patients (Rubin et al., NEJM, 2002).

Is endothelin the same as nitric oxide?

Endothelin and nitric oxide are functional opposites produced by the same cells. Endothelial cells release ET-1 to constrict blood vessels and nitric oxide to relax them. Healthy vascular function depends on the balance between these two signals. When endothelial damage reduces nitric oxide production while ET-1 remains elevated, the imbalance drives vasoconstriction, hypertension, and vascular disease. Nitric oxide also directly inhibits ET-1 gene expression, adding a regulatory layer to this balance (Davenport et al., Pharmacological Reviews, 2016).

Does endothelin cause pulmonary hypertension?

ET-1 is overproduced in the lungs and plasma of patients with pulmonary arterial hypertension and drives the vasoconstriction, smooth muscle proliferation, and fibrosis that narrow pulmonary arteries. Blocking ET-1 signaling with receptor antagonists like bosentan, ambrisentan, and macitentan is a cornerstone of PAH treatment. Macitentan reduced the combined endpoint of disease worsening or death by 45% in the SERAPHIN trial, the longest randomized controlled trial in PAH (Barton and Yanagisawa, Hypertension, 2019).

What is the difference between ETA and ETB receptors?

ETA receptors sit primarily on vascular smooth muscle cells and mediate vasoconstriction, cell growth, and fibrosis. ETB receptors sit primarily on endothelial cells and trigger nitric oxide release (causing vasodilation) and ET-1 clearance from the blood. In the kidney, ETB promotes sodium excretion. This is why selective ETA blockers like ambrisentan cause less fluid retention than dual blockers like bosentan. ET-1 and ET-2 bind both receptors equally; ET-3 prefers ETB (Inoue et al., PNAS, 1989).