is a peptide
that causes blood vessels to enlarge (dilate), and therefore causes blood pressure to lower. A class of drugs called ACE inhibitors
, which are used to lower blood pressure, increase bradykinin further lowering blood pressure. Bradykinin works on blood vessels through the release of prostacyclin, nitric oxide, and endothelial-derived hyperpolarizing factor.
Bradykinin is a physiologically and pharmacologically active peptide of the kinin group of proteins, consisting of nine amino acids.
Bradykinin is a 9-amino acid peptide chain. The amino acid
sequence of bradykinin is: Arg
. Its empirical formula is therefore C50
The kinin-kallikrein system
makes bradykinin by proteolytic cleavage
of its kininogen precursor, high-molecular-weight kininogen
(HMWK or HK), by the enzyme
In humans, bradykinin is broken down by three kininases: angiotensin-converting enzyme
(ACE), aminopeptidase P (APP), and carboxypeptidase
N (CPN), which cleave the 7-8, 1-2, and 8-9 positions, respectively .
Physiological Role (Function)
Bradykinin is a potent endothelium
, causes contraction of non-vascular smooth muscle
, increases vascular permeability
and also is involved in the mechanism of pain
. In some aspects, it has similar actions to that of histamine
, and like histamine is released from venules
rather than arterioles
Bradykinin raises internal calcium levels in neocortical astrocytes causing them to release glutamate.
Bradykinin is also thought to be the cause of the dry cough in some patients on angiotensin converting enzyme (ACE) inhibitor drugs. This refractory cough is a common cause for stopping ACE inhibitor therapy.
Overactivation of bradykinin is thought to play a role in a rare disease called Hereditary Angioedema, also known as Hereditary Angio-Neurotic Edema.
- The B1 receptor (also called bradykinin receptor B1) is expressed only as a result of tissue injury, and is presumed to play a role in chronic pain. This receptor has been also described to play a role in inflammation. . Most recently, it has been shown that the kinin B1 receptor recruits neutrophil via the chemokine CXCL5 production. Moreover, endothelial cells have been described as a potential source for this B1 receptor-CXCL5 pathway.
- The B2 receptor is constitutively active and participates in bradykinin's vasodilatory role.
The kinin B1 and B2 receptors belong to G protein coupled receptor (GPCR) family.
Bradykinin was discovered in 1948
by three Brazilian
physiologists and pharmacologists working at the Instituto Biológico
, in São Paulo
, led by Dr. Maurício Rocha e Silva
. Together with colleagues Wilson Teixeira Beraldo
and Gastão Rosenfeld
, they discovered the powerful hypotensive
effects of bradykinin in animal preparations
. Bradykinin was detected in the blood plasma
of animals after the addition of venom
extracted from the Bothrops jararaca
(Brazilian lancehead snake
), brought by Rosenfeld from the Butantan Institute
. The discovery was part of a continuing study on circulatory shock
and proteolytic enzymes
related to the toxicology
of snake bites, started by Rocha e Silva as early as 1939. Bradykinin was to prove a new autopharmacological
principle, i.e., a substance that is released in the body by a metabolic modification from precursors, which are pharmacologically active. According to B.J. Hagwood, Rocha e Silva's biographer, "The discovery of bradykinin has led to a new understanding of many physiological and pathological phenomena including circulatory shock induced by venoms and toxins."
The practical importance of the discovery of bradykinin became apparent when one of his collaborators at the Medical School of Ribeirão Preto
at the University of São Paulo, Dr. Sérgio Henrique Ferreira
, discovered a bradykinin potentiating factor
(BPF) in the bothropic venom which increases powerfully both the duration and magnitude of its effects on vasodilation and the consequent fall in blood pressure
. On the basis of this finding, Squibb
scientists developed the first of a new generation of highly-effective anti-hypertensive drugs, the so-called ACE inhibitors
, such as captopril
Currently, bradykinin inhibitors, also known as antagonists, are being developed as potential therapies for hereditary angioedema. Icatibant is one such inhibitor. Additional bradykinin inhibitors exist. It has long been known in animal studies that bromelain, a substance obtained from the stems and leaves of the pineapple plant, suppresses trauma-induced swelling caused by the release of bradykinin into the bloodstream and tissues. Other substances that act as bradykinin inhibitors include aloe and polyphenols, substances found in red wine and green tea.