Not medical advice. Talk to your provider before using any peptide.
Full disclaimer
Bradykinin9 residuesRPPGFSPFREach bubble = one amino acid. Size = residue mass. Color = chemical class.Also known as: BK, Kallidin I, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg
Fifteen seconds of plasma survival. That's the operating window for one of the most potent vasodilators the human body produces. Bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) crashes blood pressure, opens vascular gates for immune cells, and fires pain signals almost before ACE can chew it apart. Rocha e Silva first isolated this 9-amino-acid peptide in 1949. Billions of ACE inhibitor prescriptions later, cardiovascular researchers still circle back to bradykinin for answers about endothelial function and angioedema. Intra-arterial infusion at 10 to 100 nmol/min remains the gold-standard test. Nobody self-administers this peptide, and the pharmacology explains why.
Fewer than 30 seconds of plasma survival, yet decades of cardiovascular research built on top of it. Bradykinin (CAS 58-82-2, sequence Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) is a 9-amino-acid vasoactive peptide generated when kallikrein cleaves high-molecular-weight kininogen. The signaling runs through two receptors. B2 sits on vascular endothelium constitutively. When bradykinin binds, eNOS fires and prostacyclin production kicks in. Blood pressure drops. Vascular permeability increases. Pain receptors activate. Then ACE (kininase II) cleaves the Pro7-Phe8 bond and the whole signal disappears. That ACE connection is where bradykinin matters most in clinical medicine. Every ACE inhibitor prescription works partly by preventing bradykinin breakdown. The dry cough affecting a significant fraction of users? Bradykinin accumulation in pulmonary tissue. The angioedema risk? Same pathway. Chowienczyk and colleagues established the canonical human forearm protocol: intra-arterial brachial infusion at 10 to 100 nmol/min, measuring blood flow by venous occlusion plethysmography [1]. Bradykinin also sits at the center of hereditary angioedema. C1-inhibitor deficiency causes uncontrolled bradykinin production and severe episodic swelling. Icatibant, an FDA-approved B2 receptor antagonist, treats HAE attacks by blocking bradykinin directly (reviewed in the FAST-3 trial)[2]. Community self-administration does not exist; subcutaneous bioavailability lands below 5%.
Two receptors run the bradykinin program. B2 sits on vascular endothelial cells at baseline. B1 stays mostly silent until tissue injury or cytokines (IL-1-beta, TNF-alpha) flip the switch. When bradykinin docks with B2, Gaq signaling triggers phospholipase C. PLC generates IP3 and DAG from membrane phospholipids. IP3 pulls calcium from intracellular stores. That calcium spike activates eNOS; nitric oxide floods into the surrounding smooth muscle. Guanylyl cyclase converts GTP to cGMP. The muscle relaxes. The vessel dilates. A parallel arm fires simultaneously. Phospholipase A2 frees arachidonic acid. Cyclooxygenase converts it to prostacyclin (PGI2). Two vasodilatory cascades hitting at once explains why bradykinin is so potent. Bradykinin also triggers tPA release from endothelial cells. Fibrinolysis runs alongside vasodilation. On sensory neurons, B2 activation sensitizes TRPV1 channels and boosts sodium channel conductivity. Pain thresholds drop sharply. The B1 receptor tells a separate story. Des-Arg9-bradykinin, a metabolite, activates it. NF-kB signaling sustains chronic inflammation. B1 only matters during tissue injury, but once upregulated, it shifts the response from acute vasodilation toward persistent inflammatory signaling. ACE destroys bradykinin in 15 to 30 seconds (Murphey et al., J Pharmacol Exp Ther, 2000). Carboxypeptidase N strips the C-terminal arginine, producing the B1-active metabolite.
Bradykinin is one of the most extensively studied endogenous vasoactive peptides in cardiovascular and inflammatory research. Intra-arterial infusion is the established research method for assessing endothelial vasodilatory function in humans. No validated therapeutic protocol exists for exogenous administration: indirect pharmacological strategies (ACE inhibitors, kallikrein inhibitors, B2 antagonists) are the established clinical approach to the kinin system.
Chowienczyk PJ et al. "Bradykinin-induced vasodilation of human forearm resistance vessels is primarily mediated by endothelium-dependent hyperpolarization." Hypertension. 2000. PMID: 10856283.: Canonical human forearm intra-arterial bradykinin infusion methodology.
All human data involves intra-arterial or intravenous infusion under controlled conditions with continuous hemodynamic monitoring. No oral, subcutaneous, or intranasal bioavailability data exists for therapeutic use. Half-life of ~15-30 seconds makes sustained systemic exposure from any peripheral route essentially impossible without continuous infusion.
No meaningful community self-administration exists. Bradykinin does not appear in peptide community forums (Reddit r/Peptides, r/PEDs, etc.) as a self-administered compound. The ultra-short half-life, requirement for IV/IA delivery, and potent vasoactive risk profile make it impractical and dangerous outside a clinical research environment.
Community has not adopted bradykinin as a self-administered peptide. All use is confined to controlled research settings. The science is well-established for research applications; the community segment does not apply.
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 25mcg | Daily |
| Moderate | 50mcg | Daily |
| Aggressive | 100mcg | Daily |
Bradykinin isn't something you reconstitute at home with an insulin syringe. This peptide belongs in a monitored research facility with continuous blood pressure tracking and emergency airway equipment on standby. Reconstitution math for reference: a 1 mg vial with 2 mL bacteriostatic water gives 500 mcg/mL. On a 100-unit insulin syringe, each unit equals 5 mcg. A 25 mcg dose would be 5 units; 100 mcg would be 20 units. Those numbers are mostly academic, though. Research protocols use calibrated infusion pumps delivering 10 to 100 nmol/min intra-arterially, not bolus injections. The half-life situation makes bradykinin unique among peptides. At 15 to 30 seconds, you can't maintain plasma levels with intermittent dosing. Continuous infusion is the only route to sustained pharmacological effect. Subcutaneous bioavailability sits below 5% because tissue kininases destroy the peptide before it reaches systemic circulation. Source from Bachem or Sigma-Aldrich only. Grey-market peptide vendors don't have the analytical standards needed for a compound going into arteries. Verify endotoxin content below 1 EU/mg before any in vivo work.
Due to extreme vasoactive potency and risk of B1 receptor upregulation with repeated exposure, only very short research cycles are appropriate. Extended use is not recommended. Continuous hemodynamic monitoring required during administration.
Repeated B2 receptor activation causes receptor internalization and desensitization (GRK-mediated phosphorylation, β-arrestin recruitment). More importantly, repeated tissue exposure during inflammatory conditions progressively upregulates the B1 receptor (normally absent/minimal at baseline), shifting the pharmacological profile from acute vasodilation toward chronic inflammatory and pain signaling. Multi-session research designs typically space sessions ≥1 week apart to allow B1 receptor normalization.
Or use the universal Peptide Calculator for any peptide.
Expected: Dose-dependent increase in forearm blood flow demonstrating endothelium-dependent vasodilation. Used as a surrogate measure of endothelial NO and prostacyclin production capacity.
Monitor: Continuous intra-arterial blood pressure, heart rate, oxygen saturation. Vasopressor (phenylephrine) and icatibant (B2 antagonist) immediately available as rescue. Angioedema assessment at each step.
Reconstitute lyophilized bradykinin acetate with bacteriostatic water. For a 1 mg vial, adding 2 mL gives 500 mcg/mL. Add water slowly along the vial wall and swirl gently.
Transfer reconstituted solution to a calibrated syringe pump. Standard intra-arterial methodology uses dose escalation: 10 nmol/min, then 25, then 50, then 100 nmol/min. Each step runs for 6 minutes with a 10-minute washout between levels.
Establish continuous intra-arterial blood pressure monitoring before starting any infusion. IV access for fluid bolus and vasopressor support must be in place first.
Have icatibant (30 mg prefilled syringe for subcutaneous injection) and epinephrine (0.3 mg IM auto-injector) at the bedside. Standard antihistamines will not treat bradykinin-mediated angioedema.
Monitor for systolic BP drop exceeding 30 mmHg from baseline, heart rate above 120 bpm, facial or tongue swelling, or wheezing. Any trigger means immediate infusion stoppage.
After the final infusion step, monitor for at least 30 minutes. Direct peptide effects resolve within 1 to 2 minutes given the 15-second half-life, but localized edema can persist for 30 to 60 minutes.
Store reconstituted bradykinin at 2 to 8 degrees Celsius and use within 5 days. Aliquot immediately to avoid freeze-thaw degradation.
Needle gauge: not applicable for standard IA infusion protocols (delivered via catheter). For subcutaneous pain research models, 27-30 gauge insulin syringes are typical.
Syringe unit reference (1 mg / 2 mL reconstitution): 5 units = 25 mcg, 10 units = 50 mcg, 20 units = 100 mcg on a standard 100-unit insulin syringe.
Mechanistic research only: L-NG-monomethyl arginine co-infusion blocks eNOS to isolate the NO-independent component of bradykinin vasodilation. Not a therapeutic stack.
ACE is the primary enzyme degrading bradykinin (kininase II). ACE inhibitors block this degradation, dramatically prolonging and potentiating all bradykinin effects: vasodilation, angioedema risk, pain sensitization. Co-administration is dangerous and unpredictable.
Do not combineNeprilysin is a secondary bradykinin-degrading enzyme. Neprilysin inhibition further elevates bradykinin levels. Combined with exogenous bradykinin, risk of severe hypotension and angioedema markedly increased.
Do not combineARBs partially potentiate bradykinin via AT2 receptor crosstalk and may reduce bradykinin clearance. Lower severity than ACE inhibitors but still warrants caution.
Both bradykinin and VIP are potent vasodilators acting through complementary pathways (bradykinin via NO/PGI2; VIP via cAMP/adenylyl cyclase). Additive hypotensive effect with no safety data for combined use.
Do not combineSevere hypotension tops the risk profile. Bradykinin causes rapid, dose-dependent vasodilation that can crash systolic blood pressure by more than 30 mmHg within seconds of intra-arterial delivery. That speed leaves almost no time for compensatory baroreflexes. Research protocols using the Chowienczyk methodology [1] stop infusion immediately at that threshold. Angioedema is the second most dangerous concern. Bradykinin directly increases vascular permeability independent of histamine. Swelling of the face, tongue, lips, or airway can develop during or shortly after administration. The distinction matters: bradykinin-mediated angioedema does not respond to antihistamines or corticosteroids. Icatibant (30 mg subcutaneous) is the specific B2 receptor antagonist rescue agent. Epinephrine 0.3 mg intramuscular is indicated if airway compromise develops. Published research consistently reports pain and burning at the infusion site. This is direct nociceptor activation through B2 receptor sensitization of TRPV1 channels. Dose-dependent, transient, resolves within minutes of stopping the infusion. Researchers consider it confirmatory of bioactivity. Bronchoconstriction can develop, particularly in people with asthma or reactive airway disease. Bradykinin sensitizes bronchial nociceptors and triggers parasympathetic reflexes. Spirometry screening before any research exposure is standard practice. Reflexive tachycardia follows the blood pressure drop. Heart rate exceeding 120 bpm triggers protocol stoppage in most research designs. Flushing, nausea, and headache are frequent at higher infusion rates. Repeated exposure introduces a longer-term concern. B1 receptors, normally near-silent, get upregulated by inflammatory cytokines and repeated bradykinin stimulation. This shifts the pharmacological profile from acute vasodilation toward chronic NF-kB-mediated inflammatory signaling. Research protocols space sessions at least one week apart to allow B1 normalization. Mast cell activation with histamine release can layer additional allergic-type responses on top. Pregnancy is a strict contraindication; vasoactive effects may compromise placental perfusion. Concurrent ACE inhibitor use dramatically potentiates all effects by blocking bradykinin degradation. Stop administration and seek emergency care for facial swelling, tongue thickening, difficulty breathing, or sustained systolic below 80 mmHg.
Verify Bradykinin dosing and safety with a second opinion
Bradykinin is sold by biochemical research suppliers (Bachem, Sigma-Aldrich, MedChemExpress) not by peptide research vendors serving the self-administration community. Purity standards for research-grade bradykinin are typically ≥98% by HPLC, but research-chemical suppliers targeting biochemistry labs do not necessarily follow USP standards. Any impurities in an intra-arterially administered compound carry direct vascular risk. Grey-market "research peptide" vendors likely lack the analytical infrastructure to guarantee purity at the level required for vascular research.
| Test | When | Target |
|---|---|---|
| Continuous intra-arterial blood pressure | Throughout every infusion session | Systolic >90 mmHg; stop infusion if SBP drops >30 mmHg from baseline |
| Heart rate / ECG | Throughout infusion session | HR <120 bpm; stop infusion and assess if persistent tachycardia |
| Airway and angioedema assessment | Before, during, and 30 min after infusion | No visible facial, lip, tongue, or laryngeal edema |
| Forearm blood flow (venous occlusion plethysmography) | During each dose step in endothelial function research | 2–4x increase from baseline expected at 100 nmol/min IA |
| Spirometry / peak flow (if asthma history) | Before infusion session; immediately if any wheeze detected | — |
Bradykinin causes rapid, profound vasodilation: BP drop is the primary safety concern during IA/IV administration
Reflexive tachycardia expected; arrhythmia possible with severe hypotension
Bradykinin is the primary mediator of hereditary angioedema; any facial/tongue swelling requires immediate icatibant administration
Primary efficacy endpoint for vasodilatory capacity measurement
Bradykinin directly sensitizes bronchial nociceptors and can cause bronchoconstriction, particularly in atopic individuals
Immediate B2 receptor activation upon administration. Rapid onset of vasodilation, nitric oxide release, and drop in local or systemic blood pressure. Peak plasma levels achieved almost instantaneously with IV/IA delivery. Degradation by ACE begins immediately.
Maximal vasodilatory response observed. Increased vascular permeability and plasma extravasation at target tissue. Nociceptor sensitization and pain signaling detectable. Most of the administered peptide has been degraded by this point.
Hemodynamic parameters begin returning to baseline following cessation of infusion. Residual inflammatory signaling may persist via prostaglandin and NO pathways. Localized edema may take longer to resolve.
Direct peptide effects have fully dissipated. Secondary inflammatory mediators (prostaglandins, cytokines) may sustain mild local inflammation. B1 receptor upregulation begins if tissue injury or cytokine exposure is ongoing.
With repeated daily dosing in research protocols, measurable upregulation of B1 receptors at target tissue. Shift from acute B2-mediated to chronic B1-mediated signaling may alter inflammatory profile. Full vascular recovery expected within 24 hours of last dose.
0 to 30 seconds, Peak pharmacological activity: B2 receptors fire the instant bradykinin reaches the endothelium. eNOS generates nitric oxide. Vasodilation peaks within 15 to 30 seconds of intra-arterial delivery. ACE is already shredding the peptide. Flushing, burning at the infusion site, and a sharp drop in local vascular resistance happen almost simultaneously. 1 to 5 minutes, Maximal vasodilatory window: Forearm blood flow hits peak levels on plethysmography. Vascular permeability spikes at the infusion site. PGI2 and prostaglandin E2 synthesis ramp up in parallel. Over 90% of the administered peptide has been degraded by kininases. Reflexive tachycardia, headache, and possible systemic blood pressure drop if IV delivery was used. 5 to 15 minutes after infusion stops, Rapid resolution: Blood pressure and heart rate return to baseline. NO and prostacyclin production cease. Some prostaglandin signaling persists briefly. No drug accumulation between dose steps if the 10-minute washout period was honored. Residual flushing fades; localized edema may take 30 to 60 minutes to fully clear. Hours with repeated sessions, B1 receptor upregulation: B1 receptors, normally barely expressed, increase with repeated tissue exposure or inflammatory stimulation. Subsequent bradykinin exposures produce stronger inflammatory signaling through NF-kB activation. Research protocols space sessions at least a week apart to let B1 levels normalize. Amplified pain responses and shifted inflammatory profiles become the concern with repeat exposure.
Maximal B2 receptor activation. Rapid eNOS stimulation and NO release. Vasodilation peaks within 15–30 seconds of intra-arterial delivery. Simultaneous kininase II degradation begins immediately.
No community data: research setting only.
Peak forearm blood flow increase measurable by plethysmography. Vascular permeability increase at infusion site. Prostaglandin E2 and PGI2 synthesis underway. >90% of administered peptide degraded by kininases.
No community data.
Hemodynamic parameters return to baseline. NO and PGI2 production ceases. Residual prostaglandin signaling may persist briefly. No accumulation between dose steps if washout period honored.
N/A
With repeated tissue exposure or inflammatory stimulation, B1 receptor expression increases (normally near-zero at baseline). Subsequent bradykinin challenges may produce stronger inflammatory signaling via B1-mediated NF-κB activation. Relevant to multi-session research designs.
N/A
Source: Murphey et al., J Pharmacol Exp Ther, 2000: measured plasma bradykinin half-life ~15-27 seconds in humans
Loading the interactive decay curve.
Bradykinin holds research-only regulatory status. No FDA approval exists for exogenous administration as a therapeutic agent. The peptide is available from biochemical research suppliers (Bachem, Sigma-Aldrich/Merck, MedChemExpress) for investigational use. Icatibant (Firazyr), the B2 receptor antagonist used to treat hereditary angioedema, is FDA-approved. That's a bradykinin blocker, not bradykinin itself. ACE inhibitors, which raise endogenous bradykinin levels as part of their mechanism, are FDA-approved cardiovascular drugs. Direct exogenous bradykinin remains outside any approved therapeutic framework. Bradykinin does not appear on the WADA prohibited list, though this is largely irrelevant given no performance application exists. Compounding pharmacies do not produce bradykinin formulations. No pending regulatory changes affect its research-only status. Indirect modulation through approved drugs (ACE inhibitors, icatibant, lanadelumab) remains the clinical approach. This content is for informational and research purposes only. It does not constitute medical advice. Consult a qualified healthcare provider before making any decisions related to peptide research or use.
Peptide Schedule Research TeamReviewed Apr 20266 Citations
