Stress-response trigger hormone (CRF/CRH)
Natural brain hormone that starts the body's stress response by signaling the pituitary to release cortisol-triggering hormones; a research tool used to study stress, anxiety, and the adrenal system.
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
Corticotropin-releasing factor (CRF), also called corticotropin-releasing hormone (CRH), is a 41-amino-acid neuropeptide released by neurons in the hypothalamus. It is the master switch that starts the body's stress response: when the brain perceives a threat, CRF is secreted into the small portal vessels feeding the pituitary, where it tells the pituitary to release ACTH, which in turn signals the adrenal glands to make cortisol. The stored sequence here is the human/rat form (identical between the two species), which is C-terminally amidated (ends in -Ile-NH₂) — that amide is not visible in the raw one-letter sequence but is essential for receptor binding and circulating stability. CRF was the first piece of the hypothalamus-pituitary-adrenal (HPA) axis to be molecularly identified, and remains one of the most studied neuropeptides in the brain.
History
The existence of a hypothalamic factor that drives ACTH release was hypothesized in 1955 by Guillemin & Rosenberg and by Saffran & Schally, but it took more than 25 years to isolate it. The 41-residue peptide was finally characterized in 1981 by Wylie Vale, Joachim Spiess, Catherine Rivier, and Jean Rivier at the Salk Institute, who purified it from sheep hypothalamic extracts and reported the primary structure in Science (Vale et al., 1981). The human and rat forms — which differ from the ovine sequence at seven positions — were identified shortly thereafter and are identical to each other. CRF is now recognized as the prototypical member of a four-peptide family that also includes urocortin 1, urocortin 2, and urocortin 3 (Bale & Vale, Annu. Rev. Pharmacol. Toxicol., 2004).
What it does
CRF acts on two class B G-protein-coupled receptors, CRF receptor 1 (CRHR1) and CRF receptor 2 (CRHR2). Native CRF binds CRHR1 with roughly 10-fold higher affinity than CRHR2, so most of its physiological actions are CRHR1-driven (Bale & Vale, 2004). At the pituitary, CRHR1 activation triggers cAMP-mediated release of ACTH from corticotrophs, which is the classical endocrine arm of the stress response. In the brain — particularly the amygdala, locus coeruleus, and bed nucleus of the stria terminalis — CRF acts as a neuromodulator rather than a hormone, producing the behavioural side of the stress reaction: increased arousal, vigilance, anxiety-like behaviour, and suppression of feeding and reproductive drives (Ohmura et al., CNS Neurol. Disord. Drug Targets, 2009; Reul & Holsboer, Curr. Opin. Pharmacol., 2002). The CRHR2 system, by contrast, is preferentially engaged by urocortin 2 and urocortin 3 and appears to participate in dampening and resolving the stress response.
Evidence
- Human: Synthetic CRF (the human/rat sequence and the ovine sequence as a separate product) is used clinically as a diagnostic tool — the "CRH stimulation test" — to distinguish pituitary Cushing's disease from ectopic ACTH-secreting tumours and to investigate adrenal insufficiency. Ovine CRF has higher diagnostic sensitivity than human/rat CRF for Cushing's disease, attributed to slower clearance (Nieman et al., J. Clin. Endocrinol. Metab., 1989). The HPA-axis abnormalities seen in major depression and post-traumatic stress disorder are widely interpreted as CRF-system dysregulation (Reul & Holsboer, 2002; Jiang et al., Front. Cell. Neurosci., 2019).
- Animal: Central (intracerebroventricular) CRF injection in rodents reproduces a stress-like behavioural profile — heightened anxiety, reduced food intake, autonomic activation — that is reversed by CRHR1 antagonists. CRHR1 knockout mice show blunted HPA responses and reduced anxiety-like behaviour, while CRHR2 knockouts show the opposite tendency, supporting opposing roles for the two receptors (Bale & Vale, 2004).
- In vitro: Cultured anterior pituitary cells release ACTH and β-endorphin in response to CRF; this was the bioassay used in the original Vale isolation work (Vale et al., 1981).
Known effects
- Pituitary ACTH release — Mechanistically established; the basis of the clinical CRH stimulation test (Vale et al., 1981).
- Anxiety- and stress-like behaviour (central administration in animals) — Robust preclinical effect at CRHR1 (Ohmura 2009; Bale & Vale 2004).
- Appetite suppression — Preclinical; central CRF reduces food intake.
- Mood and HPA-axis dysregulation in depression — Strong correlative human evidence; CRF hyperactivity is one of the most reproducible biological findings in major depression (Reul & Holsboer 2002; Jiang 2019).
Safety signals
The clinical CRH stimulation test, in which a small intravenous dose of synthetic CRF is given, is generally well tolerated; the most commonly reported transient effects are facial flushing and a brief feeling of warmth or shortness of breath, consistent with a known vasodilatory action (Nieman 1989). Outside this narrow diagnostic indication, CRF itself is not used therapeutically. Drug-development efforts have focused on small-molecule CRHR1 antagonists (e.g. pexacerfont, verucerfont, GSK561679) for stress-related psychiatric disorders; despite a clean preclinical rationale, these have largely failed to demonstrate efficacy in clinical trials for depression, generalized anxiety disorder, or alcohol craving (Kwako et al., Neuropsychopharmacology, 2015).
Regulatory status
- US: Synthetic human CRF (corticorelin, ovine sequence under the brand name Acthrel) is FDA-approved as a diagnostic agent for distinguishing pituitary versus ectopic causes of ACTH-dependent Cushing's syndrome. It is not approved for any therapeutic indication.
- EU: Synthetic CRF is similarly available in several jurisdictions as a diagnostic peptide for the CRH stimulation test; it is not an approved therapy.
- WADA: CRF and its receptor-active analogs fall under S2 (peptide hormones, growth factors, related substances and mimetics) of the WADA Prohibited List by virtue of being a corticotropin-releasing factor that drives endogenous ACTH and cortisol.
Related peptides
CRF is the founding member of a four-peptide mammalian family that also includes urocortin 1 (binds both CRHR1 and CRHR2), urocortin 2 (CRHR2-selective), and urocortin 3 (CRHR2-selective). The urocortins are the peptides typically used experimentally when investigators want to engage CRHR2 selectively, in contrast to CRF's CRHR1 preference (Bale & Vale, 2004).
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 the chemical modification at the very tip of this stress hormone doing active receptor-binding work, not just protecting the molecule from degradation?
If the amide cap is a genuine binding element, chemists could copy or improve it to make more effective and longer-lasting drugs for conditions driven by the stress hormone system, including anxiety, PTSD, and Cushing's disease.
Do the handful of amino-acid differences between human and sheep CRF explain why human CRF targets mainly the anxiety-driving stress receptor while the sheep version is less choosy?
Mapping these differences would give scientists a precise recipe for engineering synthetic stress hormones that activate only the desired receptor, accelerating the development of more targeted treatments for stress, anxiety, and HPA-axis disorders.
Is the stress hormone CRF actually better matched to the anxiety-driving receptor than the recovery receptor it has been labeled as targeting?
Getting the target annotation right matters for every research study that builds on it. A correction here could prevent misinterpretation of hundreds of experiments linking CRF to stress disorders, depression, and anxiety.
Does the stress hormone CRF trigger the brain's own immune cells to eliminate the protective insulating cells that are missing in depressed patients' brains?
If stress hormones directly trigger brain inflammation, anti-CRF drugs could protect brain structure in psychiatric patients, a completely new way of thinking about and treating depression and bipolar disorder that goes beyond adjusting mood-related chemical signals.
Does the brain's main stress hormone, when overactive for too long, destroy the insulating cells in emotional brain regions, and could blocking it stop that damage?
If this mechanism is confirmed, doctors might be able to identify depressed patients with brain-cell damage using brain imaging, then treat them with CRF receptor blockers to prevent further damage, a precision approach that could help the roughly 30% of patients who do not respond to current antidepressants.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.800086498260498 | openfold3-mlx |
| ranking score | 0.8714042901992798 | openfold3-mlx |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.709 | global PDE — lower = better |
| disorder | 0.173 | fraction disordered |
| chain pair ipTM (A, B) | 0.800 | interface quality |
▸3-letter notation
▸recipeopenfold3-mlx 0.3.1
| parameter | value |
|---|---|
| model | openfold3-mlx 0.3.1 |
| weights | aedd8f3eb814e392… |
| hardware | apple_m4_base_16gb |
| mlx version | 0.31.1 |
| python | 3.14.3 |
| random seed | 42 |
| msa strategy | colabfold |
| diffusion samples | 1 |
| runtime | 350s |
| predicted by | mlx@peptide |
| predicted at | 2026-04-22 |
python3 openfold3/run_openfold.py predict --query_json {query.json} --runner_yaml examples/example_runner_yamls/mlx_runner.yml --output_dir {output_dir} --num_diffusion_samples 1 ▸citationbibtex
@peptide{pep10650,
sequence = {SEEPPISLDLTFHLLREVLEMARAEQLAQQAHSNRKLMEII},
target = {crhr2},
author = {peptidemodel},
year = {2026},
status = {synthesized}
}