Mechanism of Action
CRHR1 and CRHR2 Receptor Subtypes
CRH signals through two Gs-coupled GPCRs. CRHR1 (pituitary, limbic system, frontal cortex) mediates acth/" class="wiki-internal-link">ACTH release and the anxiogenic effects of stress. CRHR2 (hypothalamus, brainstem, heart, skeletal muscle) mediates the anxiolytic and cardioprotective actions of urocortins and late-phase stress adaptation. Both receptors activate adenylyl cyclase and PKA, with additional MAPK/ERK signaling. The relative activation of CRHR1 versus CRHR2 determines whether the net response is anxiogenic or anxiety-resolving.
HPA Axis Activation
CRH released from the paraventricular nucleus (PVN) into the portal circulation reaches pituitary corticotrophs, activating CRHR1 and stimulating POMC cleavage to produce ACTH. ACTH travels to the adrenal cortex, stimulating cortisol synthesis and secretion. Cortisol then provides negative feedback to the hypothalamus and pituitary, suppressing further CRH and ACTH release. Disruption of this feedback loop underlies hypercortisolism in Cushing's disease and in chronic stress.
Research Summary
Diagnostic Use
HumanThe CRH stimulation test (IV ovine or human CRH) evaluates pituitary ACTH reserve and differentiates Cushing's disease (pituitary adenoma, responds to CRH) from ectopic ACTH (often does not respond). This endocrine diagnostic test is FDA-approved and widely used in endocrinology practice.
Depression and Anxiety
HumanCSF CRH levels are elevated in major depression, PTSD, and anxiety disorders. CRHR1 antagonists (antalarmin, R121919, verucerfont) produced antidepressant and anxiolytic effects in Phase II trials without the side effects of cortisol suppression drugs. Several programs demonstrated proof-of-concept but have not yet reached Phase III.
IBS and Gut-Brain Axis
HumanPeripheral CRH mediates stress-induced gut hypermotility and visceral hypersensitivity in IBS. CRH injection in healthy subjects accelerates colonic transit and triggers pain similar to IBS. CRHR1 antagonists reduced stress-induced colonic motility in IBS patients in Phase II trials, validating the gut-brain CRH axis as an IBS target.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| HPA axis diagnostic test | 1 mcg/kg (up to 100 mcg) | Single IV dose | Intravenous |
| Stress/anxiety research | 50-100 mcg | Single IV dose | Intravenous (human challenge model) |
CRH diagnostic use is well established. Research uses IV or ICV CRH to model acute stress responses. Therapeutic development targets CRHR1 antagonism rather than CRH agonism.
Interactions
Safety Profile
Diagnostic IV CRH causes transient facial flushing, mild tachycardia, and a brief sensation of warmth lasting 1-2 minutes. These effects resolve spontaneously. No serious adverse events have been identified in the decades of diagnostic CRH test use. Research-dose CRH infusions in anxiety challenge studies are well tolerated in healthy volunteers with appropriate monitoring. CRHR1 antagonists in clinical trials have shown acceptable tolerability with no significant cortisol suppression at anxiolytic doses.
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]Owens MJ, Nemeroff CB. Physiology and pharmacology of corticotropin-releasing factor. Pharmacol Rev. 1991.
- [3]Emplit A, et al. CRF-1 antagonists and treatment of depression and anxiety: current status. CNS Drugs. 2013.