Bradykinin is a 9 amino acid peptide chain. The amino acid sequence of bradykinin is: Arg - Pro - Pro - Gly - Phe - Ser - Pro - Phe - Arg.The kinin-kallikrein system makes bradykinin by proteolytic cleavage of its kininogen precursor, high-molecular weight kininogen, by the enzyme kallikrein. ACE inhibitors prevent ACE from degrading bradykinin, which accumulates in the lungs and acts as an irritant and provokes coughing. In humans, bradykinin is broken down by three kininases: angiotensin-converting enzyme, aminopeptidase P, and carboxypeptidase N, which cleave the 7-8, 1-2, and 8-9 positions, respectively.Bradykinin is a potent endothelium-dependent vasodilator, 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.
