Bradykinin: Physiology and What Research Reports

Bradykinin is a short peptide of nine amino acids (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) that belongs to a family of signalling molecules called kinins. It is not stored in tissue in a ready-made form; instead it is cleaved out of a larger precursor protein, kininogen, by enzymes called kallikreins whenever the contact system or tissue kallikrein pathway is activated. A physiology overview described bradykinin as an inflammatory mediator that produces vasodilation, increased vascular permeability, smooth muscle effects and pain signalling, and noted that it is rapidly degraded by kininases including angiotensin-converting enzyme (ACE) (PMID 30725872).

This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about health, symptoms or treatment. Nothing here describes a protocol, and no human use is suggested.

Where Bradykinin Comes From

The kallikrein–kinin system is usually described as two arms. The plasma arm begins when factor XII contacts a negatively charged surface, activating plasma kallikrein, which liberates bradykinin from high-molecular-weight kininogen. The tissue arm uses tissue kallikrein acting on low-molecular-weight kininogen to produce kallidin (Lys-bradykinin), which aminopeptidases convert to bradykinin. The physiology review summarised this generation and the downstream vasodilatory and permeability effects, and described the peptide's very short circulating half-life because of enzymatic breakdown (PMID 30725872).

Degradation matters as much as production. ACE is one of the principal enzymes that inactivates bradykinin, which is why the peptide is discussed alongside ACE-inhibitor pharmacology. A review of bradykinin-mediated angioedema summarised how impaired degradation or excess generation of bradykinin underlies angioedema that does not respond to antihistamines, and described hereditary forms linked to C1-inhibitor deficiency alongside drug-associated forms (PMID 32113689).

Receptors and Signalling

Bradykinin acts through two G-protein-coupled receptors. The B2 receptor is constitutively expressed on endothelium, smooth muscle and neurons and binds bradykinin itself; the B1 receptor is largely induced during inflammation and responds preferentially to des-Arg metabolites. A modular signalling map assembled from the literature catalogued bradykinin-mediated inflammatory signalling, describing the receptor-linked molecules and pathway modules that connect kinin receptor activation to inflammatory gene and protein responses (PMID 34714516).

A broader research update reviewed emerging topics in kinin biology, including receptor pharmacology, cross-talk with other mediator systems and the range of physiological and pathological processes in which bradykinin has been implicated (PMID 21859431).

Quick reference

Pain and Sensory Neurons: What Studies Report

Bradykinin is one of the classic algogenic (pain-producing) mediators. An experimental review examined how bradykinin both excites and sensitises nociceptors, summarising receptor mechanisms, second-messenger pathways and the shift in receptor contribution during inflammation (PMID 19396590). More recent work characterised bradykinin receptor expression in human sensory neurons and reported bradykinin-mediated sensitisation of those neurons, extending rodent findings toward human tissue (PMID 37703419).

Reflex responses have also been studied. A rat study delivered capsaicin and bradykinin into the pericardial space and reported that the two agents induced different cardiac-somatic and cardiovascular reflex patterns, a model used to study how cardiac afferents signal (PMID 27318425).

Airway, Vascular and Platelet Observations

Cough is a well-known kinin-linked response. A guinea pig pharmacology study characterised bradykinin-evoked coughing and examined which receptor and ion-channel mechanisms contributed to the cough response (PMID 27000801). This animal work is frequently cited when discussing why bradykinin accumulation is associated with cough in ACE-inhibitor pharmacology.

Bradykinin has also been studied in haemostasis. A human study reported that bradykinin and its metabolite bradykinin 1-5 inhibited thrombin-induced platelet aggregation, indicating that a breakdown fragment retained biological activity (PMID 16772538). That finding is one reason researchers distinguish intact bradykinin from its metabolites when interpreting assays.

Cardiac Models

Preclinical cardiovascular work has examined bradykinin in injury models. One study reported that bradykinin attenuated endothelial-mesenchymal transition following cardiac ischemia-reperfusion injury, describing a protective signalling effect on endothelial phenotype (PMID 38574840). A separate rat study of myocardial infarction reported that bradykinin-(1-9) mitigated autophagy through upregulation of PI3K/Akt signalling (PMID 37060829). These were animal and cell-level investigations, and the authors described mechanisms rather than clinical outcomes.

How Bradykinin Is Measured

Because bradykinin is degraded within seconds, measuring it accurately is technically demanding: sample handling can generate or destroy the peptide before analysis. Researchers developed a liquid chromatography–tandem mass spectrometry (LC-MS/MS) assay and used it to determine plasma bradykinin concentrations during septic shock, a setting in which kinin generation has long been suspected (PMID 30802439). Mass-spectrometry approaches allow intact bradykinin to be distinguished from fragments such as bradykinin 1-5, which is relevant given that the metabolite itself showed activity in platelet studies (PMID 16772538).

Effects and Adverse Events: What Studies Report

Bradykinin is not used as a consumer peptide, and the literature summarised here concerns physiology, animal models, isolated tissue and clinical measurement rather than supplementation. The effects most consistently reported are the ones expected of an inflammatory mediator:

• Vasodilation and vascular permeability — described as core actions with rapid enzymatic inactivation (PMID 30725872).
• Swelling / angioedema — a 2020 review summarised bradykinin-mediated angioedema, including hereditary and drug-related mechanisms that are not antihistamine-responsive (PMID 32113689).
• Pain and sensitisation — reported excitation and sensitisation of nociceptors (PMID 19396590) and sensitisation of human sensory neurons (PMID 37703419).
• Cough — characterised pharmacologically in guinea pigs (PMID 27000801).

Why the Term Appears in Peptide Reading

Readers encounter bradykinin in three recurring contexts: as a textbook example of a peptide generated on demand by proteolysis rather than secreted from a vesicle; as the explanation given for cough and angioedema in discussions of ACE-inhibitor pharmacology, since ACE degrades it (PMID 30725872); and as a signalling node in inflammation mapping work (PMID 34714516). Understanding it clarifies why peptide half-life, metabolite activity and receptor induction are recurring themes across peptide science.

References

• Physiology, Bradykinin (StatPearls, 2026)
• A modular map of Bradykinin-mediated inflammatory signaling network (Journal of Cell Communication and Signaling, 2022)
• Bradykinin attenuates endothelial-mesenchymal transition following cardiac ischemia-reperfusion injury (European Journal of Pharmacology, 2024)
• Bradykinin-(1-9) mitigates autophagy through upregulating PI3K/Akt in rats with myocardial infarction (Biochemical and Biophysical Research Communications, 2023)
• Bradykinin receptor expression and bradykinin-mediated sensitization of human sensory neurons (Pain, 2024)
• Intrapericardial capsaicin and bradykinin induce different cardiac-somatic and cardiovascular reflexes in rats (Autonomic Neuroscience, 2016)
• Plasma bradykinin concentrations during septic shock determined by a novel LC-MS/MS assay (Clinica Chimica Acta, 2019)
• Pharmacology of Bradykinin-Evoked Coughing in Guinea Pigs (Journal of Pharmacology and Experimental Therapeutics, 2016)
• Update on bradykinin-mediated angioedema in 2020 (Therapie, 2020)
• Excitation and sensitization of nociceptors by bradykinin: what do we know? (Experimental Brain Research, 2009)
• Bradykinin and its metabolite bradykinin 1-5 inhibit thrombin-induced platelet aggregation in humans (Journal of Pharmacology and Experimental Therapeutics, 2006)
• New topics in bradykinin research (Allergy, 2011)