1. One of a group of peptides, occurring in blood, that are involved in inflammation and regulating blood pressure. Kinins are formed in response to blood-vessel injury by the splitting of blood plasma globulins (kininogens) by the enzyme kallikrein at the site of inflammation. Kinins include bradykinin and kallidin. They cause local increases in the permeability of small blood vessels and are also potent vasodilators that act to reduce blood pressure. Other roles have been identified in cell proliferation and migration, and in oedema formation. They mediate their effects by binding to two classes of G-protein-coupled receptors, B1 and B2 receptors. Bradykinin is a potent stimulator of pain in the skin.