Mechanism of Action
Delta-Opioid Receptor Selectivity
Deltorphin I (YAFGYPS-NH2) and Deltorphin II (YAMFYPS-NH2) bind delta-opioid receptors with Ki values of 1-4 nM and selectivity >1000-fold over MOR and KOR. The D-amino acid at position 2 is critical: it adopts a bioactive conformation and prevents enzymatic cleavage by aminopeptidases that rapidly degrade typical endogenous opioids.
Downstream Signaling
DOR activation by deltorphin inhibits adenylyl cyclase via Gi/Go proteins, reducing cAMP levels. This modulates neuronal excitability, inhibits voltage-gated calcium channels, and opens inwardly rectifying potassium channels (GIRK). At spinal and supraspinal levels, this produces analgesia, anxiolysis, and antidepressant-like effects distinct from mu-opioid receptor activation.
Research Summary
Analgesia Without Respiratory Depression
PreclinicalA key research interest is that DOR-selective analgesia produces less respiratory depression than MOR agonists. Deltorphin and DOR agonists derived from it have been explored as leads for opioid analgesics with improved safety profiles. Tolerance development also appears slower at DOR than MOR in rodent models.
Mood and Stress
PreclinicalDelta-opioid activation produces anxiolytic and antidepressant effects in rodent models, including forced swim and elevated plus maze tests. Deltorphin II ICV administration reduces stress-induced anhedonia. This has driven interest in DOR agonists for anxiety and depression treatment.
Cardioprotection
PreclinicalDelta-opioid receptor activation, including by deltorphin, has been shown to reduce cardiac ischemia-reperfusion injury in rodent models. The mechanism involves KATP channel opening and PKC activation in cardiomyocytes, mirroring endogenous ischemic preconditioning pathways.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Analgesia (rodent) | 1-10 ug/kg ICV | Single injection | Intracerebroventricular |
| Anxiolysis/antidepressant (rodent) | 5-20 ug/kg IP | Single or daily x 5 | Intraperitoneal |
| Cardioprotection (ex vivo) | 10-100 nM (perfusate) | Pre-ischemia infusion | Coronary perfusate |
No human clinical protocols. Deltorphins are pharmacological tools for delta-opioid receptor biology, not clinical compounds.
Interactions
Safety Profile
No human safety data. Deltorphins are research reagents. DOR activation in rodents causes convulsions at high doses. Unlike MOR agonists, deltorphin does not produce significant respiratory depression at analgesic doses in rodents, which is a safety advantage in theory. No human dosing or toxicology data exists.
References
- [1]Erspamer V, et al. Deltorphins: a family of naturally occurring peptides with high affinity and selectivity for delta opioid binding sites. Proc Natl Acad Sci USA. 1989;86(13):5188-5192.
- [2]Gaveriaux-Ruff C, Kieffer BL. Delta opioid receptor analgesia: recent contributions from pharmacology and molecular approaches. Behav Pharmacol. 2011;22(5-6):405-414.
- [3]Brandt MR, et al. Delta opioid receptors and the stress response. Prog Neuropsychopharmacol Biol Psychiatry. 2001;25(4):729-741.