Kinins and their receptors in hyperalgesia

Kinins (bradykinin, kallidin) are produced at sites of injury and inflammation and serve a critical role in signaling tissue distress as well as organising tissue responsiveness to injury. The acute activation and prolonged sensitization of fine afferents, to produce pain and hyperalgesia, are important in the protective responses that occur to minimize further tissue injury. These effects occur via activation of B2 receptors present on sensory neurons, resulting in a change of membrane excitability and altered cellular neurochemistry. B2 receptor activation of a variety of tissues including postganglionic sympathetic fibres stimulates the production of several proinflammatory mediators, including prostanoids and cytokines, which interact with kinins and contribute to inflammation and hyperalgesia. Increased expression of B1 receptors plays a prominent role in inflammatory hyperalgesia, but further characterization of the cellular mechanism is required. A role for kinins and kinin receptors in central pathophysiologies (trauma, ischemia, infection) needs examination. The evidence for modulation of nociception and central pain generation is compelling, as central bradykinin administration causes hyperalgesia, whereas B2 antagonists are antinociceptive. The basis for these effects should be urgently investigated. Such data will add further support to the utilization of bradykinin receptor antagonists for the treatment of peripheral and central pain.