Bradykinin is an inflammatory mediator.
It is a physiologically and pharmacologically active peptide of the kinin group of proteins, consisting of nine amino acids.

There are two forms of bradykinin receptors: B1 and B2. B1 is less present constitutively, but may be upregulated in chronic inflammation. B2 receptors are abundant in most tissues.
Stimulation of these receptors activate C polymodal receptors and cause nociception.

Bradykinin has important peripheral action in nociception.

Suzuki R, Sikandar S, Dickenson AH. Nociception: basic principles. In: Bruera ED, Portenoy RK (eds). Cancer Pain Assessment and Management. Cambridge University Press. Cambridge 2010. p. 6.