Urotensin-2: most powerful blood-vessel-narrowing peptide in the human body
A natural peptide made mainly in the kidneys and spinal cord that powerfully tightens blood vessels and affects the heart; used as a research tool to study cardiovascular disease.
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Endogenous peptide — produced naturally and routinely synthesized for research
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Endogenous peptide — receptor binding and activity established in published literature
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What this is
Urotensin-II (U-II) is a small cyclic peptide produced naturally in the human body — primarily in the kidneys and spinal cord — that acts on blood vessels and the heart. It is best known as the most potent mammalian vasoconstrictor yet identified, meaning it narrows blood vessels more powerfully than any other peptide of its kind, including endothelin-1 (Ames and colleagues, Nature, 1999). Despite originating from a gene called UTS2, it is structurally unrelated to most vasoactive peptides; it instead belongs to a family first discovered in fish decades before its human form was recognized.
The stored sequence ETPDCFWKYCV represents the 11-residue human form. Critically, the peptide's biological activity depends on a disulfide bridge linking the two cysteine residues (positions 5 and 10 of this sequence), which creates a cyclic hexapeptide ring — the C-terminal CFWKYC loop — that is the essential pharmacophore. This ring structure is not visible in the flat linear sequence but is indispensable for receptor binding (Merlino and colleagues, Journal of Amino Acids, 2013).
History
Urotensin-II was first characterized in the 1960s from the urophysis — a neuroendocrine gland at the tail of the teleost fish Gillichthys mirabilis — where it was studied for its role in salt and water balance (Merlino and colleagues, 2013). Its sequence from goby fish was published in 1980 in the Proceedings of the National Academy of Sciences, revealing structural resemblance to the hormone somatostatin.
For two decades, U-II was regarded as a fish neuropeptide with uncertain relevance to human physiology. That changed in 1999 when Ames and colleagues (Nature, 1999) identified the human form of the peptide and matched it to an "orphan" G-protein-coupled receptor — one whose ligand had previously been unknown — called GPR14. When human U-II was applied to isolated primate arteries, it caused vasoconstriction approximately ten times more potent than endothelin-1, which had until then been the benchmark for potent mammalian vasoconstrictors. This discovery prompted a wave of research into whether U-II plays a role in cardiovascular diseases.
A related peptide, urotensin-II-related peptide (URP), was subsequently identified in rat brain by Sugo and colleagues (Biochem Biophys Res Commun, 2003). URP shares the same conserved C-terminal CFWKYC ring and binds the UT receptor with comparable affinity, but has a distinct N-terminal sequence and is expressed predominantly in gonads and placenta rather than the cardiovascular system (Castel and colleagues, Frontiers in Endocrinology, 2017).
What it does
U-II acts primarily on the UT receptor (also called GPR14, encoded by the UTS2R gene) to produce powerful constriction of large blood vessels and increase the force of heart contractions. Its cardiovascular effects are context-dependent: in large primate arteries it is a potent vasoconstrictor, while in small resistance vessels it can instead trigger vasodilation through nitric oxide release from the inner vessel lining (Zhu and colleagues, British Journal of Pharmacology, 2006).
Beyond the vasculature, U-II stimulates the growth of vascular smooth muscle cells, promotes fibrosis in the heart, and has neuromodulatory activity in the brainstem and spinal cord — where it increases arousal and motor activity when given centrally in animal models (Maguire and Davenport, 2002).
Evidence
- Human: Plasma U-II is detectably elevated in patients with congestive heart failure, renal failure, and atherosclerosis compared with healthy controls, though results across studies are inconsistent (Zhu and colleagues, 2006; Russell, Vascular Health and Risk Management, 2008). In forearm infusion experiments in humans, U-II produced dose-dependent reductions in blood flow, confirming physiological vasoconstrictor activity in vivo (Maguire and Davenport, 2002). No registered clinical trials on ClinicalTrials.gov have tested U-II as a therapeutic agent.
- Animal: Chronic U-II infusion in rats increased left ventricular collagen deposition (fibrosis) and impaired contractility (Zhu and colleagues, 2006). In rat models of arterial restenosis following balloon angioplasty, the UT receptor antagonist SB-611812 reduced the intima-to-media ratio by approximately 60%, suggesting the U-II/UT axis drives pathological vessel remodelling (Zhu and colleagues, 2006). In rodent kidneys, intravenous U-II infusion increased renal blood flow and sodium excretion through a nitric oxide-dependent mechanism (Zhu and colleagues, 2006).
- In vitro: U-II contracts isolated arterial rings with an EC50 below 1 nM in primate tissue, roughly ten times more potent than endothelin-1 (Merlino and colleagues, 2013). In isolated human right atrial trabeculae, U-II increased contractile force with an EC50 of approximately 0.3 nM — compared with approximately 3.0 nM for endothelin-1 under the same conditions — and, unlike endothelin-1, did not cause arrhythmias or prolong relaxation (Maguire and Davenport, 2002). U-II also drives proliferation of vascular smooth muscle cells through synergistic signalling with oxidized LDL and serotonin (Zhu and colleagues, 2006).
Known effects
- Vasoconstriction (large arteries) — Demonstrated in primate and human tissue in vitro; forearm blood-flow reduction confirmed in human subjects (Maguire and Davenport, 2002)
- Positive inotropy (heart) — Increased contractile force in isolated human atrial muscle (Maguire and Davenport, 2002)
- Vasodilation (small resistance vessels) — Endothelium-dependent, nitric oxide-mediated; demonstrated in rat mesenteric and renal arteries (Zhu and colleagues, 2006)
- Vascular smooth muscle proliferation — Preclinical; proposed contributor to atherosclerosis and restenosis (Zhu and colleagues, 2006)
- Cardiac fibrosis — Preclinical (rat model); increased collagen deposition with chronic infusion (Zhu and colleagues, 2006)
- Renal sodium/water handling — Increased glomerular filtration rate and urinary sodium excretion in rat models; nitric oxide-dependent (Zhu and colleagues, 2006)
- Central nervous system activity — Neuromodulatory; increased rearing, grooming, and motor activity following intracerebroventricular administration in animals (Maguire and Davenport, 2002)
Safety signals
U-II is an endogenous peptide and has not been developed as a therapeutic drug. No clinical safety data from controlled human trials exists. Elevated circulating U-II has been observed — variably — in heart failure, renal failure, hypertension, atherosclerosis, and type-2 diabetes, though whether elevated U-II is a cause or a consequence of these conditions remains unresolved (Zhu and colleagues, 2006; Tsoukas and colleagues, Frontiers in Pharmacology, 2011). Measurement of plasma U-II is complicated by a roughly 1,000-fold variation in reported values across different assay methodologies, making cross-study comparisons difficult (Zhu and colleagues, 2006).
Regulatory status
- US: Not approved by the FDA; not a registered drug or biologic.
- EU: Not approved by the EMA.
- WADA: Not listed on the WADA prohibited list.
- Research status: Active area of preclinical investigation; UT receptor antagonists (including palosuran and SB-706375) have been evaluated in animal models but none has advanced to approved drug status as of 2026 (Tsoukas and colleagues, 2011).
Mechanism
U-II binds the UT receptor — a Class A (rhodopsin-family) G-protein-coupled receptor encoded by UTS2R on chromosome 17q25.3 — primarily through the conserved C-terminal CFWKYC ring, with the Trp-Lys-Tyr triad being particularly critical for receptor engagement (Merlino and colleagues, 2013). The receptor activates multiple downstream pathways depending on tissue context (Castel and colleagues, 2017):
- Gq/PLC/IP₃/Ca²⁺: The predominant vasoconstrictor pathway; phospholipase C activation releases calcium from intracellular stores and opens L-type calcium channels, driving smooth muscle contraction.
- Gα₁₃/Rho/ROCK: Rho kinase activation increases calcium sensitivity of contractile proteins, sustaining and amplifying contraction without requiring further calcium influx.
- ERK/MAPK: Mediates the mitogenic effects on vascular smooth muscle cells — proliferation and hypertrophy — that underlie the proposed role in atherosclerosis and restenosis.
- Gi/o and nitric oxide (endothelium): In endothelial cells, UT receptor activation couples to nitric oxide synthase, producing vasodilation that opposes smooth muscle constriction. This pathway dominates in small resistance vessels, explaining the paradoxical vasodilatory responses seen in some vascular beds.
The UT receptor shares structural features with chemokine receptors, including a conserved proline at position 2.58 in transmembrane domain 2 that creates a kink influencing ligand-binding geometry (Castel and colleagues, 2017). U-II binds in a pseudo-irreversible manner with slow dissociation, which prolongs receptor activation and contributes to the sustained nature of its vasoconstrictive responses.
Related peptides
- Urotensin-II-related peptide (URP) — Paralog sharing the C-terminal CFWKYC pharmacophore; identified in rat brain (Sugo and colleagues, 2003); predominantly expressed in gonads and placenta; binds the same UT receptor with similar affinity.
- Somatostatin (/card/pep-04430) — Structurally homologous cyclic peptide; the UT receptor belongs to the same GPCR superfamily as somatostatin receptors. Note: the pep-04430 link should be verified against the platform before publishing.
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
Does the dangling N-terminal part of urotensin-II change which internal signal the receptor sends, not just whether it binds?
If true, doctors could design drugs that block only the harmful vessel-narrowing signal while leaving beneficial heart-protective signals intact, reducing side effects in people with heart failure or high blood pressure.
Could urotensin-II released by diseased kidneys travel to the heart and directly cause the scarring that kills people with kidney disease?
If so, a single drug blocking urotensin-II could protect both the blood vessels and the heart muscle in kidney disease patients, potentially reducing the number one cause of death in that group.
Could urotensin-II tighten blood vessels in the heart but have a different or opposite effect in the kidneys?
If confirmed, this would explain why urotensin-II studies have given conflicting results and could open a path to drugs targeting only the harmful vessel narrowing without disrupting kidney function in patients with cardiovascular disease.
Urotensin-II is already known to activate two somatostatin receptors (sst2 and sst5) because the two peptides share a ring shape. Do some of its brain and hormone effects actually come from those receptors rather than its own receptor?
If part of urotensin-II's nervous-system action runs through somatostatin receptors, then some effects now blamed on its main receptor would need rethinking, and analogs could be useful in tumors that carry many somatostatin receptors.
Could replacing the fragile sulfur bridge in urotensin-II with a stronger chemical link make a drug that stays active in damaged, inflamed heart tissue?
People with heart failure or clogged arteries have high levels of chemicals that break down sulfur bonds, so a tougher version of this peptide could work more reliably in exactly the patients who need treatment most.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9282427430152893 | boltz-2 |
| ranking score | 0.7634943723678589 | boltz-2 |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 1.259 | global PDE — lower = better |
| disorder | NaN | fraction disordered |
▸3-letter notation
▸recipeboltz-2 1.0
| parameter | value |
|---|---|
| model | boltz-2 1.0 |
| weights | — |
| hardware | nvidia_nim_api |
| mlx version | — |
| python | — |
| random seed | — |
| msa strategy | none |
| diffusion samples | 1 |
| runtime | — |
| predicted by | mlx@peptide |
| predicted at | 2026-04-24 |
▸citationbibtex
@peptide{pep04477,
sequence = {ETPDCFWKYCV},
target = {uts2r},
author = {peptidemodel},
year = {2026},
status = {bioassayed}
}