Bradykinin is a nonapeptide that functions as a potent vasodilator and mediator of inflammation. It is part of the kallikrein-kinin system.
Synthesis:
Prekallikrein Activation: Kallikrein converts high-molecular-weight kininogen to bradykinin.
Regulation: Degraded by angiotensin-converting enzyme (ACE), which is why ACE inhibitors increase bradykinin levels.
Functions:
Vasodilation: Causes blood vessels to dilate, lowering blood pressure.
Increased Vascular Permeability: Leads to edema and inflammation.
Pain Induction: Stimulates sensory nerves to produce pain.
Smooth Muscle Contraction: Influences bronchoconstriction and gastrointestinal motility.
Receptors of Bradykinin:
B1 Receptors: Induced during inflammation; involved in chronic inflammatory responses.
B2 Receptors: Constitutively expressed; mediate most of the acute effects of bradykinin.
Clinical Relevance:
ACE Inhibitors Side Effects: Increased bradykinin levels are associated with the cough and angioedema seen in some patients.
Potential Therapeutic Targets: Modulating bradykinin pathways for treating inflammatory diseases and pain.