Pig spinal-cord peptide that tightens muscle and dulls pain (Neuromedin U-8, porcine)
A short peptide first found in pig spinal cord that tightens smooth muscle (like in the gut and uterus), tweaks brain signaling, and dulls pain; it also latches onto a receptor that is overactive in most pancreatic cancers. Used only as a laboratory research tool, not a medicine.
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
What this is
Neuromedin U-8 (NmU-8) is an 8-amino-acid peptide first isolated from porcine spinal cord in 1985. It is the shorter of two forms of Neuromedin U identified in pigs — the other, NmU-25, contains the NmU-8 sequence intact at its C-terminus. The name "neuromedin" reflects its neuronal origin, and the "U" denotes its potent ability to contract uterine smooth muscle in rats (Minamino et al. 1985). NmU-8 is a research tool used to probe the biology of Neuromedin U receptors and, in the oncology context, an oncogenic signaling axis involving the neurotensin receptor 1 (NTSR1). The stored sequence YFLFRPRN represents the backbone; the active form carries a C-terminal amide (–NH₂) on the asparagine, a post-translational modification that is essential for receptor binding and is absent from the raw sequence shown here.
History
Neuromedin U-8 and its longer sibling Neuromedin U-25 were purified by Minamino, Kangawa, and Matsuo from porcine spinal cord and reported in 1985 (Minamino et al., Biochemical and Biophysical Research Communications). Their discovery came as part of a broader search for novel neuropeptides with smooth-muscle-stimulating activity in the spinal cord — the same search that identified several other neuromedins around the same period. The "U-8" and "U-25" designations indicate peptide length (8 and 25 residues, respectively). NmU-25 contains paired arginine residues immediately upstream of the NmU-8 sequence, pointing to a common precursor that is processed by prohormone convertases. Specific G-protein-coupled receptors for Neuromedin U — NMUR1 (peripherally expressed) and NMUR2 (centrally expressed) — were not identified until around 2000, over a decade after the peptides themselves were discovered. The NmU-25 human sequence was later found to be highly conserved across mammals, with the five C-terminal residues identical across all characterized species.
What it does
Neuromedin U-8 reproduces the core biological activities of the full-length NmU-25 because its C-terminal heptapeptide (shared with NmU-25) contains all the determinants required for receptor activation. In the periphery, NmU acts on NMUR1 to contract smooth muscle — including uterine, vascular, and gastrointestinal muscle — and to modulate gastric emptying and gut motility. In the brain, NmU acts via NMUR2 to suppress food intake and increase energy expenditure; mice lacking NmU develop obesity, while mice overexpressing it are lean and eat less. Centrally, NmU activates corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus, triggering stress-axis responses and contributing to the suppression of appetite. NmU also modulates pain perception: mice lacking NMUR2 show impaired nociceptive responses. In addition, NmU influences dopamine circuit activity in the brain. In the oncology context, NmU has been found overexpressed in several tumor types, where it can drive cancer cell proliferation and invasion via distinct receptor-mediated pathways.
Evidence
- Human: No clinical trials of Neuromedin U-8 have been registered on ClinicalTrials.gov. NmU-8 is used as a pharmacological research tool and is not in clinical development. Human relevance comes from studies showing that the NmU signaling axis (via NMUR1, NMUR2, and in certain cancers a GHSR1b/NTSR1 heterodimer) is conserved and that NmU overexpression is documented in human tumor samples.
- Animal: Rodent studies have established NmU's role in energy homeostasis: central NmU administration reduces food intake and body weight; NmU-knockout mice become obese; NmU-overexpressing mice are hypophagic and lean. NMUR2-knockout mice show blunted nociceptive responses. Peripheral NmU administration decreases gastric emptying and modulates insulin secretion.
- In vitro: NmU-8, as the minimally active fragment of NmU, is used in cell-based assays to activate NMUR1 and NMUR2 signaling (Gq/11 pathway: phospholipase C activation and intracellular calcium release; Go pathway: adenylyl cyclase inhibition). In cancer cell lines, NmU increases proliferation, migration, and invasion, with pancreatic cancer studies implicating the HGF/c-Met pathway downstream of NMUR1.
Mechanism
NmU-8 is an agonist at two class A GPCRs: NMUR1 (predominantly peripheral — intestine, pancreas, lung, immune tissues) and NMUR2 (predominantly central — hypothalamus, hippocampus, spinal cord). Both receptors couple to Gq/11, activating phospholipase C and raising intracellular calcium, as well as to Go, inhibiting adenylyl cyclase. The C-terminal amide on Asn-8 is required for high-affinity receptor engagement; removing it sharply reduces potency.
The platform assigns NmU-8 to NTSR1, which reflects a distinct oncogenic context: in non-small-cell lung carcinoma, NmU was found to signal not through NMUR1 or NMUR2 but through a heterodimer of the growth hormone secretagogue receptor splice variant GHSR1b and NTSR1. This heterodimer elevates cAMP (rather than calcium) and drives tumor cell proliferation. NTSR1 is independently overexpressed at high rates in pancreatic ductal adenocarcinoma (PDAC), where it promotes tumor growth and metastasis via MAPK and NF-κB signaling. The NmU/NTSR1 axis in lung cancer and the independent NTSR1-overexpression story in PDAC are thus two separate but convergent threads that make NTSR1 the relevant target anchor for this card.
Structurally, NTSR1 is a well-characterized class A GPCR. White and colleagues (Nature, 2012) resolved the crystal structure of NTSR1 in the agonist-bound state, revealing the conformational changes driving receptor activation. Deluigi and colleagues (Science Advances, 2021) extended this by solving NTSR1 complexes with small-molecule full agonists, partial agonists, and inverse agonists, providing structural determinants that distinguish each pharmacological class — work directly relevant to understanding how ligands including peptide tools like NmU-8 engage the receptor.
Known effects
- Smooth muscle contraction — Established in vitro and in vivo (uterine, vascular, gastrointestinal)
- Appetite suppression / anti-obesity — Preclinical (rodent models); NmU-deficient mice develop obesity; NmU-overexpressing mice are lean
- Energy expenditure increase — Preclinical; central NmU raises body temperature and locomotor activity
- HPA axis activation / stress response — Preclinical; NmU activates CRH neurons and elevates corticosterone
- Pain modulation — Preclinical; NMUR2 knockout impairs nociceptive responses
- Tumor-promoting activity (cancer context) — Preclinical and human tissue data; NmU overexpressed in pancreatic and lung cancers
Related peptides
- Neuromedin U-25 — The 25-residue full-length form containing the NmU-8 sequence at its C-terminus; the precursor fragment from which NmU-8 is derived by prohormone convertase cleavage (Minamino et al. 1985).
- Neurotensin — The endogenous agonist for NTSR1; a 13-residue neuropeptide. The NmU/GHSR1b/NTSR1 oncogenic axis places NmU in mechanistic proximity to neurotensin biology at the receptor level, though the two peptides are structurally unrelated.
- Neuromedin N — A 6-residue neurotensin-related peptide encoded on the same pro-neurotensin/neuromedin N precursor as neurotensin; processed differentially by tissue-specific prohormone convertases (Kitabgi 2006). Distinct lineage from Neuromedin U.
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.
Is Neuromedin U-8 incorrectly catalogued as acting on the neurotensin receptor when it actually works through its own distinct receptor family?
Correct receptor annotation is the foundation of drug development. If researchers design NmU-8-based drugs aiming at the neurotensin receptor, they would be targeting the wrong protein, wasting resources and potentially missing therapeutic opportunities in the neurology and cancer fields where the true NmU receptors are relevant.
Could this spinal cord peptide quiet the overactive nerve pain circuits in conditions like diabetic neuropathy or post-injury chronic pain, without involving opioid receptors at all?
Neuropathic pain affects roughly 10% of adults and responds poorly to opioid drugs. A non-opioid peptide painkiller derived from the body's own spinal cord chemistry could help millions of neuropathic pain patients who currently have no good treatment options, without any addiction risk.
Do the three fatty amino acids in a row inside NmU-8 act as a size filter, fitting into the brain receptor but being too bulky for the gut receptor?
Drugs that activate only the brain form of a receptor avoid the gut side effects, like muscle contractions and cramps, that plague drugs activating both versions. If this peptide is naturally CNS-selective, it could inspire cleaner drugs for central nervous system conditions including neuropathic pain, stress disorders, and potentially eating disorders.
Does the presence or absence of a single chemical cap on the end of this peptide determine whether it triggers a calcium signal versus a different internal messenger in cells?
If one chemical modification switches between two completely different internal cell signals, it could explain why the same receptor produces different effects in different tissues and could be exploited to design tissue-specific drugs for conditions like obesity, pain, or cancer where the NmU receptor is involved.
Could a modified version of this peptide form a near-permanent grip on its receptor, making it useful as a tool for precisely mapping where that receptor is located in the nervous system?
Scientists cannot currently measure exactly where and how densely NmU receptors sit in the pain-processing spinal cord without radioactive tracers. A non-radioactive peptide that locks onto the receptor would enable safer, more detailed maps of pain receptor distribution in human tissue, accelerating the development of targeted pain therapies.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.9542521238327026 | boltz-2 |
| ranking score | 0.6085836291313171 | boltz-2 |
▸3-letter notation
▸recipeboltz-2 2.2.1
| parameter | value |
|---|---|
| model | boltz-2 2.2.1 |
| weights | — |
| hardware | vast_v100_32gb |
| mlx version | — |
| python | — |
| random seed | 1 |
| msa strategy | colabfold_local |
| runtime | — |
| predicted by | — |
| predicted at | 2026-05-22 |
▸citationbibtex
@peptide{pep10697,
sequence = {YFLFRPRN},
target = {ntsr1},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}