Quick summary
Kyotorphin (Tyr-Arg) is the simplest known neuroactive peptide -- just two amino acids -- yet produces potent analgesia by stimulating met-enkephalin release rather than binding opioid receptors directly.
Overview
Kyotorphin (Tyr-Arg) is an endogenous analgesic dipeptide isolated from bovine brain in 1979. It is one of the simplest known neuroactive peptides — just two amino acids — yet produces potent naloxone-reversible analgesia when administered centrally. Kyotorphin is concentrated in synaptosomes of pain-relevant brain regions and is synthesized by a dedicated kyotorphin synthase from tyrosine and arginine. It binds a distinct G protein-coupled receptor and may act as an endogenous opioid modulator rather than a direct opioid receptor agonist.
Mechanism of action
Kyotorphin does not directly bind classical mu, delta, or kappa opioid receptors with high affinity. Its analgesic effect appears to be mediated indirectly: kyotorphin stimulates the release of met-enkephalin from nerve terminals, which then acts on delta and mu opioid receptors to produce analgesia. A specific kyotorphin receptor (KTP-R) coupled to a Gi-type G protein has been proposed but is not yet definitively identified. Kyotorphin is unevenly distributed in the brain, concentrated in the midbrain, pons/medulla, and dorsal spinal cord — regions with the highest sensitivity to morphine analgesia — consistent with a physiological role in pain modulation.
Dosing protocols
| Purpose | Route | Dosage | Frequency | Notes |
|---|---|---|---|---|
| analgesia research (central administration, animal) | intravenous | 1–100 nmol | per experimental session (often intracisternal or ICV in animal models) |
Dosing information is for educational purposes only. Consult a qualified healthcare professional before using any peptide.
Research summary
Kyotorphin research peaked in the 1980s–1990s and has seen renewed interest with the identification of its receptor and potential for antimicrobial applications. Central administration produces dose-dependent analgesia blocked by naloxone, confirming opioid-pathway involvement. Brain regional distribution studies place it in major pain processing nodes. More recent research has explored kyotorphin analogs with improved blood-brain barrier penetration and resistance to peptidase cleavage. Antimicrobial properties against bacterial membranes have also been reported. No therapeutic agents derived from kyotorphin have advanced to clinical trials.[1][2][3]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with Kyotorphin for synergistic effects.
Legal status
Kyotorphin is available for laboratory research only. It has no approved clinical applications.
Sourcing & access
Research compound
Kyotorphin is classified as a research compound. Regulatory status varies by jurisdiction. Always verify current legal status and source from vendors providing third-party certificates of analysis (COA).
Frequently asked questions
Kyotorphin (Tyr-Arg) is an endogenous analgesic dipeptide isolated from bovine brain in 1979. It is one of the simplest known neuroactive peptides, consisting of just two amino acids, yet produces potent pain relief. It is concentrated in brain regions with the highest sensitivity to morphine analgesia.
Kyotorphin does not directly bind classical opioid receptors with high affinity. Instead, it stimulates the release of met-enkephalin from nerve terminals, which then acts on delta and mu opioid receptors to produce analgesia. A specific kyotorphin receptor coupled to a Gi-type G protein has been proposed but not definitively identified.
Kyotorphin is a research-only compound with no well-characterized adverse effects in humans. Animal models show sedation at high doses. Its very short half-life of 2-5 minutes due to rapid hydrolysis by dipeptidases limits persistent effects.
Kyotorphin is remarkable for producing opioid-mediated analgesia with just two amino acids, making it the smallest known analgesic peptide. Recent research has also explored kyotorphin analogs with improved blood-brain barrier penetration as well as potential antimicrobial properties against bacterial membranes.