Bradykinin
Introduction
Bradykinin is a naturally occurring neuropeptide. Bradykinin is vasoactive,
meaning it acts to alter the physiological state, especially the tone and
calibre, of a vessel. Enzymes known as kininogens enzymically form bradykinin
and it is very similar to the peptide kallidin. The enzyme facilitates the
production of bradykinin, a nonapeptide, from the precursor prekallikrein,
which is found the plasma in an inactive form of the precursor of kallikrein.
When activated kallikrein uses the substrate kininogen, which is a plasma
-globulin
of high molecular weight, to form bradykinin by ‘cutting’ it from
the larger protein sequence.
This whole process is often activated by a blood factor, the Hageman factor; factor XII of the clotting process, which is the main mechanism in the setting in of inflammation when there is exposure to negative surfaces such as those found on collagen and basement membrane that are often exposed in injury. The presence of these stimulating factors is exasperated in inflammation when vascular permeability is increased, leading to further expose of the plasma to negative surfaces. [1, 8, 41]
