Mechanism of Action
CRH Receptors and HPA Axis
CRH acts via two GPCRs: CRHR1 (predominantly in the pituitary and brain) and CRHR2 (peripheral tissues, brainstem, heart). CRHR1 is Gs-coupled and mediates pituitary acth/" class="wiki-internal-link">ACTH release. Both receptors activate adenylyl cyclase, increasing cAMP and PKA activity. In the pituitary, this drives POMC gene transcription and ACTH secretion, triggering adrenal cortisol production.
Extra-HPA Roles
CRH acts in the amygdala and prefrontal cortex to mediate anxiety, fear consolidation, and the behavioral response to stress. Peripheral CRH in the gut modulates motility and visceral pain. CRH in skin is pro-inflammatory. CRHR2 in the heart mediates vasodilation and cardiac contractility modulation. These diverse roles make CRH a pleiotropic stress integrator beyond its pituitary function.
Research Summary
CRH Stimulation Test
Standard of CareThe ovine or human CRH stimulation test (1 ug/kg IV) is used to distinguish pituitary from ectopic ACTH-dependent Cushing's syndrome. In pituitary Cushing's, CRH causes an exaggerated ACTH and cortisol rise; ectopic sources typically do not respond. Acthrel (corticorelin ovine triflutate) is FDA-approved for this diagnostic indication.
Anxiety and Depression
Preclinical/ClinicalCRH hypersecretion is documented in major depressive disorder and PTSD (elevated CSF CRH). CRH receptor antagonists (CRH-1 antagonists) have been extensively tested in clinical trials for anxiety and depression. Despite strong preclinical support, most CRHR1 antagonists have failed to show robust clinical efficacy, possibly due to the redundancy of stress circuits.
Inflammatory Bowel Disease
PreclinicalCRH in the gut (peripheral CRH system) contributes to stress-induced gut motility changes and visceral hypersensitivity in IBS and IBD. CRHR1 antagonists reduce stress-induced colonic motor responses in rodents. This peripheral CRH axis is a therapeutic target for stress-related GI disorders.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| CRH stimulation test (Cushing's diagnosis) | 1 ug/kg IV (max 100 ug) | Single dose | Intravenous |
| HPA axis activation (rodent) | 1-10 ug ICV | Single injection | Intracerebroventricular |
| Anxiety model (rodent) | 0.3-1 ug ICV | Single injection | Intracerebroventricular |
CRH is used diagnostically in clinical practice. Therapeutic applications are under investigation but no approved therapeutic indications exist beyond diagnostic use.
Interactions
Safety Profile
Single-dose IV CRH for diagnostic testing causes transient flushing, warmth, and mild cortisol elevation; rarely anaphylaxis. Chronic CRH elevation (as in Cushing's disease or severe depression) causes HPA hyperactivation with all its downstream consequences. CRHR1 antagonists tested clinically show generally good tolerability but variable efficacy. No WADA concerns for diagnostic CRH testing.
References
- [1]Vale W, et al. Characterization of a 41-residue ovine hypothalamic peptide that stimulates secretion of corticotropin and beta-endorphin. Science. 1981;213(4514):1394-1397.
- [2]Nemeroff CB. The role of corticotropin-releasing factor in the pathogenesis of major depression. Pharmacopsychiatry. 1988;21(2):76-82.
- [3]Hauger RL, et al. International Union of Pharmacology. XXXVI. Current status of the nomenclature for receptors for corticotropin-releasing factor and their ligands. Pharmacol Rev. 2003;55(1):21-26.